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Arenaviruses, a family of negative-sense RNA viruses spread by rodents, are a leading cause of severe hemorrhagic fever in humans. Due to a paucity of antivirals and vaccines for arenaviruses, there is a need to identify new mechanisms for interfering with arenavirus replication. In several negative-sense RNA viruses, natural viral interference results from the production of non-standard viral genomes (nsVGs) that activate the innate immune system and/or compete for essential viral products. Although it is well established that arenaviruses produce strong interfering activities, it is unknown if they produce interfering nsVGs. Here, we show that arenaviruses produce deletions within the intergenic region of their small (S) RNA genome, and these deletions inhibit viral glycoprotein production during minigenome replication. S RNA deletions are more abundant when arenaviruses are grown in high-interfering conditions and are associated with reduced viral replication. Overall, we found that arenaviruses produce internal deletions within the S RNA intergenic region that are capable of decreasing glycoprotein production. These natural arenavirus interfering molecules provide a new target for the generation of therapeutics against arenaviruses.IMPORTANCEArenaviruses are hemorrhagic fever-causing pathogens that infect millions of people a year. There are currently no approved antivirals that target arenaviruses, and understanding natural mechanisms that inhibit arenavirus replication is crucial for the development of effective therapeutics. Here, we identified multiple deletions within arenavirus genomes that remove major replicative elements of the viral genomes. We show that deletions that remove the intergenic region of the viral genome can prevent viral protein production. These deletions were found in all arenaviruses tested in this study representing a mechanism that could be harnessed for the development of antivirals that broadly target the arenavirus family., Competing Interests: The authors declare no conflict of interest.

The COVID-19 outbreak has highlighted the importance of pandemic preparedness for the prevention of future health crises. One virus family with high pandemic potential are Arenaviruses, which have been detected almost worldwide, particularly in Africa and the Americas. These viruses are highly understudied and many questions regarding their structure, replication and tropism remain unanswered, making the design of an efficacious and molecularly-defined vaccine challenging. We propose that structure-driven computational vaccine design will contribute to overcome these challenges. Computational methods for stabilization of viral glycoproteins or epitope focusing have made progress during the last decades and particularly during the COVID-19 pandemic, and have proven useful for rational vaccine design and the establishment of novel diagnostic tools. In this review, we summarize gaps in our understanding of Arenavirus molecular biology, highlight challenges in vaccine design and discuss how structure-driven and computationally informed strategies will aid in overcoming these obstacles., Competing Interests: Declaration of competing interest C.T.S. has received unrelated research funds from Navigo Protein GmbH, Halle (Saale), Germany. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

In a recent article published in Immunology & Cell Biology, Dalit et al. describe how correcting mutations in the C57BL/6 mouse strain can restore production of the chemokine CXCL11, although surprisingly, this expression of CXCL11 had little effect on B and T cells and the innate immune response to infection with lymphocytic choriomeningitis virus or influenza virus., (© 2022 Australian and New Zealand Society for Immunology, Inc.)

Upon virus infection, CD8 + T cell accumulation is tightly controlled by simultaneous proliferation and apoptosis. However, it remains unclear how TCR signal coordinates these events to achieve expansion and effector cell differentiation. We found that T cell-specific deletion of nuclear helicase Dhx9 led to impaired CD8 + T cell survival, effector differentiation, and viral clearance. Mechanistically, Dhx9 acts as the key regulator to ensure LCK- and CD3ε-mediated ZAP70 phosphorylation and ERK activation to protect CD8 + T cells from apoptosis before proliferative burst. Dhx9 directly regulates Id2 transcription to control effector CD8 + T cell differentiation. The DSRM and OB_Fold domains are required for LCK binding and Id2 transcription, respectively. Dhx9 expression is predominantly increased in effector CD8 + T cells of COVID-19 patients. Therefore, we revealed a previously unknown regulatory mechanism that Dhx9 protects activated CD8 + T cells from apoptosis and ensures effector differentiation to promote antiviral immunity independent of nuclear sensor function.

CD8+ T cells play a crucial role in the control and resolution of viral infections and can adopt a wide range of phenotypes and effector functions depending on the inflammatory context and the duration and extent of antigen exposure. Similarly, viral infections can exert diverse selective pressures on populations of clonally related T cells. Technical limitations have nevertheless made it challenging to investigate the relationship between clonal selection and transcriptional phenotypes of virus-specific T cells. We therefore performed single-cell T cell receptor (TCR) repertoire and transcriptome sequencing of virus-specific CD8 T cells in murine models of acute, chronic and latent infection. We observed clear infection-specific populations corresponding to memory, effector, exhausted, and inflationary phenotypes. We further uncovered a mouse-specific and polyclonal T cell response, despite all T cells sharing specificity to a single viral epitope, which was accompanied by stereotypic TCR germline gene usage in all three infection types. Persistent antigen exposure during chronic and latent viral infections resulted in a higher proportion of clonally expanded T cells relative to acute infection. We furthermore observed a relationship between transcriptional heterogeneity and clonal expansion for all three infections, with highly expanded clones having distinct transcriptional phenotypes relative to less expanded clones. Together our work relates clonal selection to gene expression in the context of viral infection and further provides a dataset and accompanying software for the immunological community., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Kuhn, Sandu, Agrafiotis, Hong, Shlesinger, Neimeier, Merkler, Oxenius, Reddy and Yermanos.)

A specialized and fine-tuned immune response of bats upon infection with viruses is believed to provide the basis for a "friendly" coexistence with these pathogens, which are often lethal for humans and other mammals. First insights into the immunity of bats suggest that bats have evolved to possess their own strategies to cope with viral infections. Yet, the molecular details for this innocuous coexistence remain poorly described and bat infection models are the key to unveiling these secrets. In Jamaican fruit bats (Artibeus jamaicensis) , a New World bat species, infection experiments with its (putative) natural viral pathogens Tacaribe virus (TCRV), rabies virus (RABV), and the bat influenza A virus (IAV) H18N11, have contributed to an accurate, though still incomplete, representation of the bat-imposed immunity. Surprisingly, though many aspects of their innate and adaptive immune responses differ from that of the human immune response, such as a contraction of the IFN locus and reduction in the number of immunoglobulin subclasses, variations could also be observed between Jamaican fruit bats and other bat species.

RIG-I and MDA5 are major cytoplasmic innate-immune sensor proteins that recognize aberrant double-stranded RNAs generated during virus infection to activate type 1 interferon (IFN-I) and IFN-stimulated gene (ISG) expressions to control virus infection. The roles of RIG-I and MDA5 in controlling replication of Pichinde virus (PICV), a mammarenavirus, in mice have not been examined. Here, we showed that MDA5 single knockout (SKO) and RIG-I/MDA5 double knockout (DKO) mice are highly susceptible to PICV infection as evidenced by their significant reduction in body weights during the course of the infection, validating the important roles of these innate-immune sensor proteins in controlling PICV infection. Compared to the wildtype mice, SKO and DKO mice infected with PICV had significantly higher virus titers and lower IFN-I expressions early in the infection but appeared to exhibit a late and heightened level of adaptive immune responses to clear the infection. When a recombinant rPICV mutant virus (rPICV-NPmut) that lacks the ability to suppress IFN-I was used to infect mice, as expected, there were heightened levels of IFN-I and ISG expressions in the wild-type mice, whereas infected SKO and DKO mice showed delayed mouse growth kinetics and relatively low, delayed, and transient levels of innate and adaptive immune responses to this viral infection. Taken together, our data suggest that PICV infection triggers activation of immune sensors that include but might not be necessarily limited to RIG-I and MDA5 to stimulate effective innate and adaptive immune responses to control virus infection in mice., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Brisse, Huang, Rahman, Di, Liang and Ly.)

Siglec-H is a DAP12-associated receptor on plasmacytoid dendritic cells (pDCs) and microglia. Siglec-H inhibits TLR9-induced IFN-α production by pDCs. Previously, it was found that Siglec-H-deficient mice develop a lupus-like severe autoimmune disease after persistent murine cytomegalovirus (mCMV) infection. This was due to enhanced type I interferon responses, including IFN-α. Here we examined, whether other virus infections can also induce autoimmunity in Siglec-H-deficient mice. To this end we infected Siglec-H-deficient mice with influenza virus or with Lymphocytic Choriomeningitis virus (LCMV) clone 13. With both types of viruses we did not observe induction of autoimmune disease in Siglec-H-deficient mice. This can be explained by the fact that both types of viruses are ssRNA viruses that engage TLR7, rather than TLR9. Also, Influenza causes an acute infection that is rapidly cleared and the chronicity of LCMV clone 13 may not be sufficient and may rather suppress pDC functions. Siglec-H inhibited exclusively TLR-9 driven type I interferon responses, but did not affect type II or type III interferon production by pDCs. Siglec-H-deficient pDCs showed impaired Hck expression, which is a Src-family kinase expressed in myeloid cells, and downmodulation of the chemokine receptor CCR9, that has important functions for pDCs. Accordingly, Siglec-H-deficient pDCs showed impaired migration towards the CCR9 ligand CCL25. Furthermore, autoimmune-related genes such as Klk1 and DNase1l3 are downregulated in Siglec-H-deficient pDCs as well. From these findings we conclude that Siglec-H controls TLR-9-dependent, but not TLR-7 dependent inflammatory responses after virus infections and regulates chemokine responsiveness of pDCs., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Szumilas, Corneth, Lehmann, Schmitt, Cunz, Cullen, Chu, Marosan, Mócsai, Benes, Zehn, Dudziak, Hendriks and Nitschke.)

During chronic viral infections, CD8 T cells rapidly lose antiviral and immune-stimulatory functions in a sustained program termed exhaustion. In addition to this loss of function, CD8 T cells with the highest affinity for viral antigen can be physically deleted. Consequently, treatments designed to restore function to exhausted cells and control chronic viral replication are limited from the onset by the decreased breadth of the antiviral T cell response. Yet, it remains unclear why certain populations of CD8 T cells are deleted while others are preserved in an exhausted state. We report that CD8 T cell deletion during chronic viral infection can be prevented by therapeutically lowering viral replication early after infection. The initial resistance to deletion enabled long-term maintenance of antiviral cytolytic activity of the otherwise deleted high-affinity CD8 T cells. In combination with decreased virus titers, CD4 T cell help and prolonged interactions with costimulatory molecules B7-1/B7-2 were required to prevent CD8 T cell deletion. Thus, therapeutic strategies to decrease early virus replication could enhance virus-specific CD8 T cell diversity and function during chronic infection.

Arenaviruses represent a family of viruses that are naturally present in rodents belonging to subfamily Murinae, Neotominae or Sigmodontinae. Except for Lassa virus, little information is available on other Old-World arenaviruses. Here, we describe strain AnRB3214, a virus isolated from a presumed Praomys sp. rodent in the Central African Republic in 1981 and assigned to Ippy virus based on antigenic similarity. The strain was simultaneously sequenced on Illumina NovaSeq 6000 and MinION Mk1B devices and analysed with various bioinformatics tools. We show that the best genome coverage and depth were obtained with the Kaiju and Minimap2 classification and identification tools, on either the MinION or the Illumina reads. The genetic analysis of AnRB3214 fragments showed 68% to 79% similarity with the Mobala and Gairo mammarenaviruses at the nucleic acid level. Strain AnRB3214 had a truncated nucleoprotein smaller than that of other Old World arenaviruses. Molecular clock analysis suggests that this strain diverged from Mobala virus at least 400 years ago. Finally, this study illustrates the importance of genomics in the identification of archived viruses and expands on the diversity of African arenaviruses, because strain AnRB3214 is either a variant or a close relative of Mobala virus, and not Ippy virus.

Immune evasion of pathogens can modify the course of infection and impact viral persistence and pathology. Here, using different strains of the lymphocytic choriomeningitis virus (LCMV) model system, we show that slower propagation results in limited type I interferon (IFN-I) production and viral persistence. Specifically, cells infected with LCMV-Docile exhibited reduced viral replication when compared to LCMV-WE and as a consequence, infection with LCMV-Docile resulted in reduced activation of bone marrow derived dendritic cells (BMDCs) and IFN-I production in vitro in comparison with LCMV-WE. In vivo, we observed a reduction of IFN-I, T cell exhaustion and viral persistence following infection of LCMV-Docile but not LCMV-WE. Mechanistically, block of intracellular protein transport uncovered reduced propagation of LCMV-Docile when compared to LCMV-WE. This reduced propagation was critical in blunting the activation of the innate and adaptive immune system. When mice were simultaneously infected with LCMV-Docile and LCMV-WE, immune function was restored and IFN-I production, T cell effector functions as well as viral loads were similar to that of mice infected with LCMV-WE alone. Taken together, this study suggests that reduced viral propagation can result in immune evasion and viral persistence.

T cells dynamically interact with multiple, distinct cellular subsets to determine effector and memory differentiation. Here, we developed a platform to quantify cell location in three dimensions to determine the spatial requirements that direct T cell fate. After viral infection, we demonstrated that CD8 + effector T cell differentiation is associated with positioning at the lymph node periphery. This was instructed by CXCR3 signaling since, in its absence, T cells are confined to the lymph node center and alternatively differentiate into stem-like memory cell precursors. By mapping the cellular sources of CXCR3 ligands, we demonstrated that CXCL9 and CXCL10 are expressed by spatially distinct dendritic and stromal cell subsets. Unlike effector cells, retention of stem-like memory precursors in the paracortex is associated with CCR7 expression. Finally, we demonstrated that T cell location can be tuned, through deficiency in CXCL10 or type I interferon signaling, to promote effector or stem-like memory fates.

During chronic infection and cancer, a self-renewing CD8 + T cell subset maintains long-term immunity and is critical to the effectiveness of immunotherapy. These stem-like CD8 + T cells diverge from other CD8 + subsets early after chronic viral infection. However, pathways guarding stem-like CD8 + T cells against terminal exhaustion remain unclear. Here, we show that the gene encoding transcriptional repressor BACH2 is transcriptionally and epigenetically active in stem-like CD8 + T cells but not terminally exhausted cells early after infection. BACH2 overexpression enforced stem-like cell fate, whereas BACH2 deficiency impaired stem-like CD8 + T cell differentiation. Single-cell transcriptomic and epigenomic approaches revealed that BACH2 established the transcriptional and epigenetic programs of stem-like CD8 + T cells. In addition, BACH2 suppressed the molecular program driving terminal exhaustion through transcriptional repression and epigenetic silencing. Thus, our study reveals a new pathway that enforces commitment to stem-like CD8 + lineage and prevents an alternative terminally exhausted cell fate.

The kinase PDK1 is a crucial regulator for immune cell development by connecting PI3K to downstream AKT signaling. However, the roles of PDK1 in CD4 + T cell differentiation, especially in T follicular helper (Tfh) cell, remain obscure. Here we reported PDK1 intrinsically promotes the Tfh cell differentiation and germinal center responses upon acute infection by using conditional knockout mice. PDK1 deficiency in T cells caused severe defects in both early differentiation and late maintenance of Tfh cells. The expression of key Tfh regulators was remarkably downregulated in PDK1-deficient Tfh cells, including Tcf7 , Bcl6 , Icos , and Cxcr5 . Mechanistically, ablation of PDK1 led to impaired phosphorylation of AKT and defective activation of mTORC1, resulting in substantially reduced expression of Hif1α and p-STAT3. Meanwhile, decreased p-AKT also suppresses mTORC2-associated GSK3β activity in PDK1-deficient Tfh cells. These integrated effects contributed to the dramatical reduced expression of TCF1 and ultimately impaired the Tfh cell differentiation., Competing Interests: ZS, YY, MY, JL, WG, ZQ, ZW, FW, WY, SY No competing interests declared, (© 2021, Sun et al.)

Mechanistic target of rapamycin complex 1 (mTORC1) regulates CD8 + T-cell differentiation and function. Despite the links between PI3K-AKT and mTORC1 activation in CD8 + T cells, the molecular mechanism underlying mTORC1 activation remains unclear. Here, we show that both the kinase activity and the death domain of DAPK1 are required for maximal mTOR activation and CD8 + T-cell function. We found that TCR-induced activation of calcineurin activates DAPK1, which subsequently interacts with TSC2 via its death domain and phosphorylates TSC2 to mediate mTORC1 activation. Furthermore, both the kinase domain and death domain of DAPK1 are required for CD8 + T-cell antiviral responses in an LCMV infection model. Together, our data reveal a novel mechanism of mTORC1 activation that mediates optimal CD8 + T-cell function and antiviral activity.

Natural killer (NK) cells are important innate effectors that play a pivotal role in the defense against tumors and infections and participate in regulating adaptive immunity. Recent studies have revealed phenotypic and functional heterogeneity of NK cells. Here, using murine models of acute and chronic lymphocytic choriomeningitis virus infection, we observed that a CD49a + CD49b + NK cell subset emerged in the liver and other tissues, and underwent vigorous expansion following viral infection, before progressively decreasing in cell number. These viral infection-induced CD49a + CD49b + NK cells displayed an activated and mature phenotype. Moreover, compared with liver-resident NK cells and conventional NK (cNK) cells, CD49a + CD49b + NK cells showed increased functional competence, as evidenced by higher amounts of IFN-γ production and stronger cytotoxic capabilities during viral infection. Generation of these CD49a + CD49b + NK cells was shown to be independent of the T-bet transcription factor. Adoptive transfer experiments revealed that cNK cells could convert into CD49a + CD49b + NK cells following viral infection. Collectively, these results suggest that viral infection-induced CD49a + CD49b + NK cells represent a transiently activated state of cNK cells.

Immune activation within the tumor microenvironment is one promising approach to induce tumor regression. Certain viruses including oncolytic viruses such as the herpes simplex virus (HSV) and non-oncolytic viruses such as the lymphocytic choriomeningitis virus (LCMV) are potent tools to induce tumor-specific immune activation. However, not all tumor types respond to viro- and/or immunotherapy and mechanisms accounting for such differences remain to be defined. In our current investigation, we used the non-cytopathic LCMV in different human melanoma models and found that melanoma cell lines produced high levels of CCL5 in response to immunotherapy. In vivo , robust CCL5 production in LCMV infected Ma-Mel-86a tumor bearing mice led to recruitment of NK cells and fast tumor regression. Lack of NK cells or CCL5 abolished the anti-tumoral effects of immunotherapy. In conclusion, we identified CCL5 and NK cell-mediated cytotoxicity as new factors influencing melanoma regression during virotherapy., (Copyright © 2020 Bhat, Zaun, Hamdan, Lang, Adomati, Schmitz, Friedrich, Bergerhausen, Cham, Li, Ali, Zhou, Khairnar, Duhan, Brandenburg, Machlah, Schiller, Berry, Xu, Vollmer, Häussinger, Thier, Pandyra, Schadendorf, Paschen, Schuler, Lang and Lang.)

Endemic to West Africa and South America, mammalian arenaviruses can cross the species barrier from their natural rodent hosts to humans, resulting in illnesses ranging from mild flu-like syndromes to severe and fatal haemorrhagic zoonoses. The increased frequency of outbreaks and associated high fatality rates of the most prevalent arenavirus, Lassa, in West African countries, highlights the significant risk to public health and to the socio-economic development of affected countries. The devastating impact of these viruses is further exacerbated by the lack of approved vaccines and effective treatments. Differential immune responses to arenavirus infections that can lead to either clearance or rapid, widespread and uncontrolled viral dissemination are modulated by the arenavirus multifunctional proteins, NP and Z. These two proteins control the antiviral response to infection by targeting multiple cellular pathways; and thus, represent attractive targets for antiviral development to counteract infection. The interplay between the host immune responses and viral replication is a key determinant of virus pathogenicity and disease outcome. In this review, we examine the current understanding of host immune defenses against arenavirus infections and summarise the host protein interactions of NP and Z and the mechanisms that govern immune evasion strategies.

CD8 T cells play a crucial role in providing protection from viral infections. It has recently been established that a subset of CD8 T cells expressing Tcf1 are responsible for sustaining exhausted T cells during chronic lymphocytic choriomeningitis virus (LCMV) infection. Many of these studies, however, have been performed using T cell receptor (TCR) transgenic mice, in which CD8 T cells express a monoclonal TCR specific for the LCMV glycoprotein. To investigate whether the Tcf1+ and Tcf1- repertoires are naturally composed of similar or different clones in wild-type mice exposed to acute or chronic LCMV infection, we performed TCR repertoire sequencing of virus-specific CD8 T cells, including Tcf1+ and Tcf1- populations. Our analysis revealed that the Tcf1+ TCR repertoire is maintained at an equal or higher degree of clonal diversity despite harboring fewer cells. Additionally, within the same animal, there was extensive clonal overlap between the Tcf1+ and Tcf1- repertoires in both chronic and acute LCMV infection. We could further detect these virus-specific clones in longitudinal blood samples earlier in the infection. With respect to common repertoire parameters (clonal overlap, germline gene usage, and clonal expansion), we found minor differences between the virus-specific TCR repertoire of acute and chronic LCMV infection 40 days post infection. Overall, our results indicate that the Tcf1+ population emerging during chronic LCMV infection is not clonally distinct from the Tcf1- population, supporting the notion that the Tcf1+ pool is indeed a fuel for the more exhausted Tcf1- population within the heterogenous repertoire of LCMV-specific CD8 T cells., (Copyright © 2020 Yermanos, Sandu, Pedrioli, Borsa, Wagen, Oetiker, Welten, Pallmer, Reddy and Oxenius.)

Regulatory T cells (T regs ) maintain peripheral self-tolerance and limit immune mediated pathology. Like effector T cells, T regs can specialize in T H 1-dominated immune responses and co-express T-bet together with Foxp3. This allows for expression of CXCR3 and efficient homing to sites of T H 1 responses. However, whether such functional specialization is paralleled by memory generation among T regs is unknown. In this study, we investigated the ability of polyclonal T regs to form functional memory in response to viral infection. Using adoptive transfer models to compare infection-experienced T regs generated upon acute Lymphocytic Choriomeningitis Virus (LCMV) WE and Vaccinia Virus (VV) infections with naive T regs , we observed no differences in their phenotype or their in vivo maintenance. When comparing functional properties of infection-experienced and naive T regs , we found no differences in in vitro suppressive capacity nor in their ability to limit the effector response upon homologous, systemic or local re-challenge in vivo. Our results suggest that no functional T reg memory is generated in the context of systemic LCMV or VV infection, but we cannot rule out the possibility that the generation of T reg memory may be possible in other contexts.

The transcription factor STAT6 regulates gene expression in response to IL-4 and IL-13. To further investigate how activated STAT6 modulates B cells development and function in vivo, we characterized mice that express a constitutively active version specifically in B cells. CD19Cre_STAT6vt mice show spontaneous phosphorylation and nuclear translocation of STAT6 in B cells. About 80 genes were more than twofold up- or downregulated in splenic B cells from CD19Cre_STAT6vt as compared to control mice. B cell development, tissue localization, and populations of follicular and marginal zone B cells, B1 B cells, GC B cells, and plasma cells (PCs) appeared to be normal. However, the number of IgE + and IgG1 + GC B cells and PCs as well as serum IgE and IgG1 levels were increased in CD19Cre_STAT6vt mice. Infection with Lymphocytic choriomeningitis virus associated with high levels of TNF and IFN-γ did not prevent the development of a significantly increased IgE and IgG1 response against the virus in CD19Cre_STAT6vt mice. These results suggest that prolonged STAT6 activation during chronic allergic inflammation may result in IgE responses during subsequent viral or bacterial infection that could further stimulate mast cell activation even in the absence of the initial allergic response., (© 2019 The Authors. European Journal of Immunology published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Foxp3 + regulatory T (Treg) cells are essential for maintaining peripheral tolerance and preventing autoimmunity. While genetic factors may predispose for autoimmunity, additional environmental triggers, such as viral infections, are usually required to initiate the onset of disease. Here, we show that viral infection with LCMV results in type I IFN-dependent Treg cell loss that is rapidly compensated by the conversion and expansion of Vβ5 + conventional T cells into iTreg cells. Using Vβ5-deficient mice, we show that these Vβ5 + iTreg cells are dispensable for limiting anti-viral immunity. Rather, the delayed replenishment of Treg cells in Vβ5-deficient mice compromises suppression of microbiota-dependent activation of CD8 + T cells, resulting in colitis. Importantly, recovery from clinical symptoms in IBD patients is marked by expansion of the corresponding Vβ2 + Treg population in humans. Collectively, we provide a link between a viral trigger and an impaired Treg cell compartment resulting in the initiation of immune pathology.

Certain arenaviruses that circulate in rodent populations can cause life-threatening hemorrhagic fevers when they infect humans. Due to their efficient transmission, arenaviruses pose a severe risk for outbreaks and might be exploited as biological weapons. Effective countermeasures against these viruses are highly desired. Ideally, a single remedy would be effective against many or even all the pathogenic viruses in this family. However, despite the fact that all pathogenic arenaviruses from South America utilize transferrin receptor 1 (TfR1) as a cellular receptor, their viral glycoproteins are highly diversified, impeding efforts to isolate cross-neutralizing antibodies. Here we address this problem using a rational design approach to target TfR1-tropic arenaviruses with high potency and breadth. The pan-reactive molecule is highly effective against all arenaviruses that were tested, offering a universal therapeutic approach. Our design scheme avoids the shortcomings of previous immunoadhesins and can be used to combat other zoonotic pathogens.

Objective: The Fragile X mental retardation (FMR) syndrome is a frequently inherited intellectual disability caused by decreased or absent expression of the FMR protein (FMRP). Lack of FMRP is associated with neuronal degradation and cognitive dysfunction but its role outside the central nervous system is insufficiently studied. Here, we identify a role of FMRP in liver disease., Design: Mice lacking Fmr1 gene expression were used to study the role of FMRP during tumour necrosis factor (TNF)-induced liver damage in disease model systems. Liver damage and mechanistic studies were performed using real-time PCR, Western Blot, staining of tissue sections and clinical chemistry., Results: Fmr1 null mice exhibited increased liver damage during virus-mediated hepatitis following infection with the lymphocytic choriomeningitis virus. Exposure to TNF resulted in severe liver damage due to increased hepatocyte cell death. Consistently, we found increased caspase-8 and caspase-3 activation following TNF stimulation. Furthermore, we demonstrate FMRP to be critically important for regulating key molecules in TNF receptor 1 (TNFR1)-dependent apoptosis and necroptosis including CYLD, c-FLIP S and JNK, which contribute to prolonged RIPK1 expression. Accordingly, the RIPK1 inhibitor Necrostatin-1s could reduce liver cell death and alleviate liver damage in Fmr1 null mice following TNF exposure. Consistently, FMRP-deficient mice developed increased pathology during acute cholestasis following bile duct ligation, which coincided with increased hepatic expression of RIPK1, RIPK3 and phosphorylation of MLKL., Conclusions: We show that FMRP plays a central role in the inhibition of TNF-mediated cell death during infection and liver disease., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

The determinants of protective CD8+ memory T cell (CD8+TM) immunity remain incompletely defined and may in fact constitute an evolving agency as aging CD8+TM progressively acquire enhanced rather than impaired recall capacities. Here, we show that old as compared to young antiviral CD8+TM more effectively harness disparate molecular processes (cytokine signaling, trafficking, effector functions, and co-stimulation/inhibition) that in concert confer greater secondary reactivity. The relative reliance on these pathways is contingent on the nature of the secondary challenge (greater for chronic than acute viral infections) and over time, aging CD8+TM re-establish a dependence on the same accessory signals required for effective priming of naïve CD8+T cells in the first place. Thus, our findings reveal a temporal regulation of complementary recall response determinants that is consistent with the recently proposed "rebound model" according to which aging CD8+TM properties are gradually aligned with those of naïve CD8+T cells; our identification of a broadly diversified collection of immunomodulatory targets may further provide a foundation for the potential therapeutic "tuning" of CD8+TM immunity., Competing Interests: The authors have declared that no competing interests exist.

Viral infections are a natural part of our existence. They can affect us in many ways that are the result of the interaction between the viral pathogen and our immune system. Most times, the resulting immune response is beneficial for the host. The pathogen is cleared, thus protecting our vital organs with no other consequences. Conversely, the reaction of our immune system against the pathogen can cause organ damage (immunopathology) or lead to autoimmune disease. To date, there are several mechanisms for virus-induced autoimmune disease, including molecular mimicry and bystander activation, in support of the "fertile field" hypothesis (terms defined in our review). In contrast, viral infections have been associated with protection from autoimmunity through mechanisms that include Treg invigoration and immune deviation, in support of the "hygiene hypothesis", also defined here. Infection with lymphocytic choriomeningitis virus (LCMV) is one of the prototypes showing that the interaction of our immune system with viruses can either accelerate or prevent autoimmunity. Studies using mouse models of LCMV have helped conceive and establish several concepts that we now know and use to explain how viruses can lead to autoimmune activation or induce tolerance. Some of the most important mechanisms established during the course of LCMV infection are described in this short review.

Boid Inclusion Body Disease (BIBD) is a potentially fatal disease reported in captive boid snakes worldwide that is caused by reptarenavirus infection. Although the detection of intracytoplasmic inclusion bodies (IB) in blood cells serves as the gold standard for the ante mortem diagnosis of BIBD, the mechanisms underlying IB formation and the pathogenesis of BIBD are unknown. Knowledge on the reptile immune system is sparse compared to the mammalian counterpart, and in particular the response towards reptarenavirus infection is practically unknown. Herein, we investigated a breeding collection of 70 Boa constrictor snakes for BIBD, reptarenavirus viraemia, anti-reptarenavirus IgM and IgY antibodies, and population parameters. Using NGS and RT-PCR on pooled blood samples of snakes with and without BIBD, we could identify three different reptarenavirus S segments in the collection. The examination of individual samples by RT-PCR indicated that the presence of University of Giessen virus (UGV)-like S segment strongly correlates with IB formation. We could also demonstrate a negative correlation between BIBD and the presence of anti-UGV NP IgY antibodies. Further evidence of an association between antibody response and BIBD is the finding that the level of anti-reptarenavirus antibodies measured by ELISA was lower in snakes with BIBD. Furthermore, female snakes had a significantly lower body weight when they had BIBD. Taken together our findings suggest that the detection of the UGV-/S6-like S segment and the presence of anti-reptarenavirus IgY antibodies might serve as a prognostic tool for predicting the development of BIBD., Competing Interests: The authors have declared that no competing interests exist.

Several mammarenaviruses, chiefly Lassa virus (LASV) in Western Africa and Junín virus (JUNV) in the Argentine Pampas, cause severe disease in humans and pose important public health problems in their endemic regions. Moreover, mounting evidence indicates that the worldwide-distributed mammarenavirus lymphocytic choriomeningitis virus (LCMV) is a neglected human pathogen of clinical significance. The lack of licensed mammarenavirus vaccines and partial efficacy of current anti-mammarenavirus therapy limited to an off-label use of the nucleoside analog ribavirin underscore an unmet need for novel therapeutics to combat human pathogenic mammarenavirus infections. This task can be facilitated by the implementation of "drug repurposing" strategies to reduce the time and resources required to advance identified antiviral drug candidates into the clinic. We screened a drug repurposing library of 11,968 compounds (Repurposing, Focused Rescue and Accelerated Medchem [ReFRAME]) and identified several potent inhibitors of LCMV multiplication that had also strong anti-viral activity against LASV and JUNV. Our findings indicate that enzymes of the rate-limiting steps of pyrimidine and purine biosynthesis, the pro-viral MCL1 apoptosis regulator, BCL2 family member protein and the mitochondrial electron transport complex III, play critical roles in the completion of the mammarenavirus life cycle, suggesting they represent potential druggable targets to counter human pathogenic mammarenavirus infections., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Following infection, inflammatory cues upregulate core transcriptional programs to establish pathogen-specific protection. In viral infections, T follicular helper (TFH) cells express the prototypical T helper 1 transcription factor T-bet. Several studies have demonstrated essential but conflicting roles for T-bet in TFH biology. Understanding the basis of this controversy is crucial, as modulation of T-bet expression instructs TFH differentiation and ultimately protective antibody responses. Comparing influenza and LCMV viral infections, we demonstrate that the role of T-bet is contingent on the environmental setting of TFH differentiation, IL-2 signaling, and T cell competition. Furthermore, we demonstrate that T-bet expression by either TFH or GC B cells independently drives antibody isotype class switching. Specifically, T cell-specific loss of T-bet promotes IgG1, whereas B cell-specific loss of T-bet inhibits IgG2a/c switching. Combined, this work highlights that the context-dependent induction of T-bet instructs the development of protective, neutralizing antibodies following viral infection or vaccination., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Some studies show eliminating senescent cells rejuvenate aged mice and attenuate deleterious effects of chemotherapy. Nevertheless, it remains unclear whether senescence affects immune cell function. We provide evidence that exposure of mice to ionizing radiation (IR) promotes the senescent-associated secretory phenotype (SASP) and expression of p16 INK4a in splenic cell populations. We observe splenic T cells exhibit a reduced proliferative response when cultured with allogenic cells in vitro and following viral infection in vivo. Using p16-3MR mice that allow elimination of p16 INK4a -positive cells with exposure to ganciclovir, we show that impaired T-cell proliferation is partially reversed, mechanistically dependent on p16 INK4a expression and the SASP. Moreover, we found macrophages isolated from irradiated spleens to have a reduced phagocytosis activity in vitro, a defect also restored by the elimination of p16 INK4a expression. Our results provide molecular insight on how senescence-inducing IR promotes loss of immune cell fitness, which suggest senolytic drugs may improve immune cell function in aged and patients undergoing cancer treatment., (© 2019 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)

Considerable evidence indicates that autoimmune disease expression depends on both genetic and environmental factors. Among potential environmental triggers, occupational airway exposure to crystalline silica and virus infections have been linked to lupus and other autoimmune diseases in both humans and mouse models. Here, we hypothesized that combined silica and virus exposures synergize and induce autoimmune manifestations more effectively than single exposure to either of these factors, particularly in individuals with low genetic predisposition. Accordingly, infection with the model murine pathogen lymphocytic choriomenigitis virus (LCMV) in early life, followed by airway exposure to crystalline silica in adult life, induced lupus-like autoantibodies to several nuclear self-antigens including chromatin, RNP and Sm, concurrent with kidney lesions, in non-autoimmune C57BL/6 (B6) mice. In contrast, given individually, LCMV or silica were largely ineffectual in this strain. These results support a multihit model of autoimmunity, where exposure to different environmental factors acting on distinct immunostimulatory pathways complements limited genetic predisposition and increases the risk of autoimmunity above a critical threshold., (Copyright © 2019 Elsevier Inc. All rights reserved.)

This study examines the extent to which memory CD4 + T cells share immunosurveillance strategies with CD8 + resident memory T cells (T RM ). After acute viral infection, memory CD4 + T cells predominantly used residence to survey nonlymphoid tissues, albeit not as stringently as observed for CD8 + T cells. In contrast, memory CD4 + T cells were more likely to be resident within lymphoid organs than CD8 + T cells. Migration properties of memory-phenotype CD4 + T cells in non-SPF parabionts were similar, generalizing these results to diverse infections and conditions. CD4 + and CD8 + T RM shared overlapping transcriptional signatures and location-specific features, such as granzyme B expression in the small intestine, revealing tissue-specific and migration property-specific, in addition to lineage-specific, differentiation programs. Functionally, mucosal CD4 + T RM reactivation locally triggered both chemokine expression and broad immune cell activation. Thus, residence provides a dominant mechanism for regionalizing CD4 + T cell immunity, and location enforces shared transcriptional, phenotypic, and functional properties with CD8 + T cells., (© 2019 Beura et al.)

Asymmetric partitioning of fate determinants is a mechanism that contributes to T cell differentiation. However, it remains unclear whether the ability of T cells to divide asymmetrically is influenced by their differentiation state, as well as whether enforcing asymmetric cell division (ACD) rates would have an impact on T cell differentiation and memory formation. Using the murine LCMV infection model, we established a correlation between cell stemness and the ability of CD8 + T cells to undergo ACD. Transient mTOR inhibition was proven to increase ACD rates in naïve and memory cells and to install this ability in exhausted CD8 + T cells. Functionally, enforced ACD correlated with increased memory potential, leading to more efficient recall response and viral control upon acute or chronic LCMV infection. Moreover, transient mTOR inhibition also increased ACD rates in human CD8 + T cells. Transcriptional profiling revealed that progenies emerging from enforced ACD exhibited more pronounced early memory signatures, which functionally endowed these cells with better survival in the absence of antigen exposure and more robust homing to secondary lymphoid organs, providing critical access to survival niches. Our data provide important insights into how ACD can improve long-term survival and function of T cells and open new perspectives for vaccination and adoptive T cell transfer therapies., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Hemorrhagic fevers (HF) resulting from pathogenic arenaviral infections have traditionally been neglected as tropical diseases primarily affecting African and South American regions. There are currently no FDA-approved vaccines for arenaviruses, and treatments have been limited to supportive therapy and use of non-specific nucleoside analogs, such as Ribavirin. Outbreaks of arenaviral infections have been limited to certain geographic areas that are endemic but known cases of exportation of arenaviruses from endemic regions and socioeconomic challenges for local control of rodent reservoirs raise serious concerns about the potential for larger outbreaks in the future. This review synthesizes current knowledge about arenaviral evolution, ecology, transmission patterns, life cycle, modulation of host immunity, disease pathogenesis, as well as discusses recent development of preventative and therapeutic pursuits against this group of deadly viral pathogens.

T cells become dysfunctional when they encounter self antigens or are exposed to chronic infection or to the tumour microenvironment 1 . The function of T cells is tightly regulated by a combinational co-stimulatory signal, and dominance of negative co-stimulation results in T cell dysfunction 2 . However, the molecular mechanisms that underlie this dysfunction remain unclear. Here, using an in vitro T cell tolerance induction system in mice, we characterize genome-wide epigenetic and gene expression features in tolerant T cells, and show that they are distinct from effector and regulatory T cells. Notably, the transcription factor NR4A1 is stably expressed at high levels in tolerant T cells. Overexpression of NR4A1 inhibits effector T cell differentiation, whereas deletion of NR4A1 overcomes T cell tolerance and exaggerates effector function, as well as enhancing immunity against tumour and chronic virus. Mechanistically, NR4A1 is preferentially recruited to binding sites of the transcription factor AP-1, where it represses effector-gene expression by inhibiting AP-1 function. NR4A1 binding also promotes acetylation of histone 3 at lysine 27 (H3K27ac), leading to activation of tolerance-related genes. This study thus identifies NR4A1 as a key general regulator in the induction of T cell dysfunction, and a potential target for tumour immunotherapy.

Prolonged exposure of CD8 + T cells to antigenic stimulation, as in chronic viral infections, leads to a state of diminished function termed exhaustion. We now demonstrate that even during exhaustion there is a subset of functional CD8 + T cells defined by surface expression of SIRPα, a protein not previously reported on lymphocytes. On SIRPα + CD8 + T cells, expression of co-inhibitory receptors is counterbalanced by expression of co-stimulatory receptors and it is only SIRPα + cells that actively proliferate, transcribe IFNγ and show cytolytic activity. Furthermore, target cells that express the ligand for SIRPα, CD47, are more susceptible to CD8 + T cell-killing in vivo. SIRPα + CD8 + T cells are evident in mice infected with Friend retrovirus, LCMV Clone 13, and in patients with chronic HCV infections. Furthermore, therapeutic blockade of PD-L1 to reinvigorate CD8 + T cells during chronic infection expands the cytotoxic subset of SIRPα + CD8 + T cells.

Lymphocytic choriomeningitis virus (LCMV) is a paradigm-forming experimental system with a remarkable track record of contributing to the discovery of many of the fundamental concepts of modern immunology. The ability of LCMV to establish a chronic infection in immunocompetent adult mice was instrumental for identifying T cell exhaustion and this system has been invaluable for uncovering the complexity, regulators, and consequences of this state. These findings have been directly relevant for understanding why ineffective T cell responses commonly arise during many chronic infections including HIV and HCV, as well as during tumor outgrowth. The principal feature of exhausted T cells is the inability to elaborate the array of effector functions necessary to contain the underlying infection or tumor. Using LCMV to determine how to prevent and reverse T cell exhaustion has highlighted the potential of checkpoint blockade therapies, most notably PD-1 inhibition strategies, for improving cellular immunity under conditions of antigen persistence. Here, we discuss the discovery, properties, and regulators of exhausted T cells and highlight how LCMV has been at the forefront of advancing our understanding of these ineffective responses.

Apoptosis of CD8 T cells is an essential mechanism that maintains immune system homeostasis, prevents autoimmunity, and reduces immunopathology. CD8 T cell death also occurs early during the response to both inflammation and costimulation blockade (CoB). In this article, we studied the effects of a combined deficiency of Fas (extrinsic pathway) and Bim (intrinsic pathway) on early T cell attrition in response to lymphocytic choriomeningitis virus infection and during CoB during transplantation. Loss of Fas and Bim function in Bcl2l11 -/- Fas lpr/lpr mice inhibited apoptosis of T cells and prevented the early T cell attrition resulting from lymphocytic choriomeningitis virus infection. Bcl2l11 -/- Fas lpr/lpr mice were also resistant to prolonged allograft survival induced by CoB targeting the CD40-CD154 pathway. These results demonstrate that both extrinsic and intrinsic apoptosis pathways function concurrently to regulate T cell homeostasis during the early stages of immune responses and allograft survival during CoB., (Copyright © 2019 by The American Association of Immunologists, Inc.)

There is currently much interest in how different APC subsets shape the immune response. We recently described a division of labor between classical dendritic cells (cDC) and inflammatory monocyte-derived APC in provision of costimulatory ligands to T cells early during chronic lymphocytic choriomeningitis clone 13 (LCMV 13) infection in mice. At day 2 of LCMV 13 infection, cDC preferentially express CD80 and CD86, whereas TNF superfamily ligands GITRL, 4-1BBL, CD70, and OX40L are preferentially induced by type I IFN on inflammatory monocyte-derived APC, with minimal expression on cDC. In this study, we further investigate the expression of TNF and B7 family ligands on APC over the course of LCMV 13 infection. OX40L and 4-1BBL remain above baseline through the chronic stage of infection, with predominant expression on inflammatory APC compared with cDC in the spleen, partially blocked by anti-IFN-γR Ab pretreatment. Conversely, CD70, like GITRL, returns to baseline on the APC within a few days postinfection. In the lung, TNF family ligands were also preferentially expressed on inflammatory monocyte-derived APC. CD86 was generally higher on cDC than inflammatory APC in the spleen, but in the lung CD86 was highest on inflammatory APC. Moreover, in the spleen, CD80 levels on different APC subsets fluctuated over the course of the infection. We also show that LPS induction of TNF superfamily ligands is largely mediated through type I IFN. This study highlights the importance of IFNs and monocyte-derived APC in TNF superfamily ligand expression in both secondary lymphoid organs and tissues during chronic viral infection., (Copyright © 2018 The Authors.)

Infection of specific pathogen-free mice with lymphocytic choriomeningitis virus (LCMV) is a widely used model to study antiviral T-cell immunity. Infections in the real world, however, are often accompanied by coinfections with unrelated pathogens. Here we show that in mice, systemic coinfection with E. coli suppresses the LCMV-specific cytotoxic T-lymphocyte (CTL) response and virus elimination in a NK cell- and TLR2/4-dependent manner. Soluble TLR4 ligand LPS also induces NK cell-mediated negative CTL regulation during LCMV infection. NK cells in LPS-treated mice suppress clonal expansion of LCMV-specific CTLs by a NKG2D- or NCR1-independent but perforin-dependent mechanism. These results suggest a TLR4-mediated immunoregulatory role of NK cells during viral-bacterial coinfections.

Immune responses are critical for defense against pathogens. However, prolonged viral infection can result in defective T cell immunity, leading to chronic viral infection. We studied immune activation in response to arenavirus infection during cholestasis using bile duct ligation (BDL). We monitored T cell responses, virus load and liver pathology markers after infection with lymphocytic choriomeningitis virus (LCMV). BDL mice failed to induce protective anti-viral immunity against LCMV and consequently exhibited chronic viral infection. BDL mice exhibited reduced anti-viral T cell immunity as well as reduced type 1 interferon production early after LCMV infection. Consistently, the presence of serum from BDL mice reduced the responsiveness of dendritic cell (DC) and T cell cultures when compared to Sham controls. Following fractionation and mass spectrometry analyses of sera, we identified several serum factors to be upregulated following BDL including bilirubin, bile acids, 78 kDa Glucose regulated protein (GRP78) and liver enzymes. Bilirubin and GRP78 were capable of inhibiting DC and T cell activation. In this work, we demonstrate that liver damage mediated by cholestasis results in defective immune induction following arenavirus infection.

Ca 2+ release-activated Ca 2+ channel regulator 2A (CRACR2A) is expressed abundantly in T cells and acts as a signal transmitter between TCR stimulation and activation of the Ca 2+ /NFAT and JNK/AP1 pathways. CRACR2A has been linked to human diseases in numerous genome-wide association studies and was shown to be one of the most sensitive targets of the widely used statin drugs. However, the physiological role of CRACR2A in T cell functions remains unknown. In this study, using transgenic mice for tissue-specific deletion, we show that CRACR2A promotes Th1 responses and effector function of Th17 cells. CRACR2A was abundantly expressed in Th1 and Th17 cells. In vitro, deficiency of CRACR2A decreased Th1 differentiation under nonpolarizing conditions, whereas the presence of polarizing cytokines compensated this defect. Transcript analysis showed that weakened TCR signaling by deficiency of CRACR2A failed to promote Th1 transcriptional program. In vivo, conditional deletion of CRACR2A in T cells alleviated Th1 responses to acute lymphocytic choriomeningitis virus infection and imparted resistance to experimental autoimmune encephalomyelitis. Analysis of CNS from experimental autoimmune encephalomyelitis-induced mice showed impaired effector functions of both Th1 and Th17 cell types, which correlated with decreased pathogenicity. Collectively, our findings demonstrate the requirement of CRACR2A-mediated TCR signaling in Th1 responses as well as pathogenic conversion of Th17 cells, which occurs at the site of inflammation., (Copyright © 2018 by The American Association of Immunologists, Inc.)

Dendritic cells produce IL-12 and IL-23 in response to viral and bacterial infection and these cytokines are responsible for successful pathogen clearance. How sequential viral and bacterial infections affect the production of IL-12 and IL-23 is currently not known. Our study demonstrates that in dendritic cells infected with Lymphocytic choriomeningitis virus (LCMV), TLR activation with bacterial PAMPs resulted in reduced IL-12 and IL-23 expression compared to non-infected cells. Furthermore, expression of other proinflammatory cytokines, TNF-α and IL-6, were not inhibited under these conditions. We discovered that TLR-induced phosphorylation of p38 was significantly inhibited in LCMV-infected cells. We detected enhanced expression of suppressor of cytokine signalling (SOCS)-3 and IL-10. Yet, neutralizing IL-10 did not restore IL-12/IL-23 expression. Taken together, these results show that virus infection interferes with the magnitude of TLR-mediated inflammatory responses by repressing specific cytokine expression., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Several arenaviruses cause hemorrhagic fever (HF) diseases that are associated with high morbidity and mortality in humans. Accordingly, HF arenaviruses have been listed as top-priority emerging diseases for which countermeasures are urgently needed. Because arenavirus nucleoprotein (NP) plays critical roles in both virus multiplication and immune-evasion, we used an unbiased proteomic approach to identify NP-interacting proteins in human cells. DDX3, a DEAD-box ATP-dependent-RNA-helicase, interacted with NP in both NP-transfected and virus-infected cells. Importantly, DDX3 deficiency compromised the propagation of both Old and New World arenaviruses, including the HF arenaviruses Lassa and Junin viruses. The DDX3 role in promoting arenavirus multiplication associated with both a previously un-recognized DDX3 inhibitory role in type I interferon production in arenavirus infected cells and a positive DDX3 effect on arenavirus RNA synthesis that was dependent on its ATPase and Helicase activities. Our results uncover novel mechanisms used by arenaviruses to exploit the host machinery and subvert immunity, singling out DDX3 as a potential host target for developing new therapies against highly pathogenic arenaviruses., Competing Interests: The authors have declared that no competing interests exist.

Determining the magnitude of local immune response during mucosal exposure to viral pathogens is critical to understanding the mechanism of viral pathogenesis. We previously showed that vaginal inoculation of lymphocytic choriomeningitis virus (LCMV) fails to induce a robust innate immune response in the lower female reproductive tract (FRT), allowing high titer viral replication and a delay in T-cell-mediated viral control. Despite this immunological delay, LCMV replication remained confined mainly to the FRT and the draining iliac lymph node. Here, we show that rectal infection with LCMV triggers type I/III interferon responses, followed by innate immune activation and lymphocyte recruitment to the colon. In contrast to vaginal exposure, innate immunity controls LCMV replication in the colon, but virus rapidly disseminates systemically. Virus-induced inflammation promotes the recruitment of LCMV target cells to the colon followed by splenic viral dissemination by infected B cells, and to a lesser extent by CD8 T cells. These findings demonstrate major immunological differences between vaginal and rectal exposure to the same viral pathogen, highlighting unique risks associated with each of these common routes of sexual viral transmission.

Arenaviruses pose a major public health threat and cause numerous infections in humans each year. Although most viruses belonging to this family do not cause disease in humans, some arenaviruses, such as Lassa virus and Machupo virus, are the etiological agents of lethal hemorrhagic fevers. The absence of a currently licensed vaccine and the highly pathogenic nature of these viruses both make the necessity of developing viable vaccines and therapeutics all the more urgent. Arenaviruses have a single glycoprotein on the surface of virions, the glycoprotein complex (GPC), and this protein can be used as a target for vaccine development. Here, we describe immunization strategies to generate monoclonal antibodies (MAbs) that cross-react between the glycoprotein complexes of both Old World and New World arenaviruses. Several monoclonal antibodies isolated from immunized mice were highly cross-reactive, binding a range of Old World arenavirus glycoproteins, including that of Lassa virus. One such monoclonal antibody, KL-AV-2A1, bound to GPCs of both New World and Old World viruses, including Lassa and Machupo viruses. These cross-reactive antibodies bound to epitopes present on the glycoprotein 2 subunit of the glycoprotein complex, which is relatively conserved among arenaviruses. Monoclonal antibodies binding to these epitopes, however, did not inhibit viral entry as they failed to neutralize a replication-competent vesicular stomatitis virus pseudotyped with the Lassa virus glycoprotein complex in vitro In addition, no protection from virus challenge was observed in in vivo mouse models. Even so, these monoclonal antibodies might still prove to be useful in the development of clinical and diagnostic assays. IMPORTANCE Several viruses in the Arenaviridae family infect humans and cause severe hemorrhagic fevers which lead to high case fatality rates. Due to their pathogenicity and geographic tropisms, these viruses remain very understudied. As a result, an effective vaccine or therapy is urgently needed. Here, we describe efforts to produce cross-reactive monoclonal antibodies that bind to both New and Old World arenaviruses. All of our MAbs seem to be nonneutralizing and nonprotective and target subunit 2 of the glycoprotein. Due to the lack of reagents such as recombinant glycoproteins and antibodies for rapid detection assays, our MAbs could be beneficial as analytic and diagnostic tools., (Copyright © 2018 Amanat et al.)

New World arenaviruses cause fatal hemorrhagic disease in South America. Pirital virus (PIRV), a mammarenavirus hosted by Alston’s cotton rat ( Sigmodon alstoni ), causes a disease in Syrian golden hamsters ( Mesocricetus auratus ) (biosafety level-3, BSL-3) that has many pathologic similarities to the South American hemorrhagic fevers (BSL-4) and, thus, is considered among the best small-animal models for human arenavirus disease. Here, we extend in greater detail previously described clinical and pathological findings in Syrian hamsters and provide evidence for a pro-inflammatory macrophage response during PIRV infection. The liver was the principal target organ of the disease, and signs of Kupffer cell involvement were identified in mortally infected hamster histopathology data. Differential expression analysis of liver mRNA revealed signatures of the pro-inflammatory response, hematologic dysregulation, interferon pathway and other host response pathways, including 17 key transcripts that were also reported in two non-human primate (NHP) arenavirus liver-infection models, representing both Old and New World mammarenavirus infections. Although antigen presentation may differ among rodent and NHP species, key hemostatic and innate immune-response components showed expression parallels. Signatures of pro-inflammatory macrophage involvement in PIRV-infected livers included enrichment of Ifng , Nfkb2 , Stat1 , Irf1 , Klf6 , Il1b , Cxcl10 , and Cxcl11 transcripts. Together, these data indicate that pro-inflammatory macrophage M1 responses likely contribute to the pathogenesis of acute PIRV infection.

Regulatory T cells (Tregs) play a cardinal role in the immune system by suppressing detrimental autoimmune responses, but their role in acute, chronic infectious diseases and tumor microenvironment remains unclear. We recently demonstrated that IFN-α/β receptor (IFNAR) signaling promotes Treg function in autoimmunity. Here we dissected the functional role of IFNAR-signaling in Tregs using Treg-specific IFNAR deficient (IFNARfl/flxFoxp3YFP-Cre) mice in acute LCMV Armstrong, chronic Clone-13 viral infection, and in tumor models. In both viral infection and tumor models, IFNARfl/flxFoxp3YFP-Cre mice Tregs expressed enhanced Treg associated activation antigens. LCMV-specific CD8+ T cells and tumor infiltrating lymphocytes from IFNARfl/flxFoxp3YFP-Cre mice produced less antiviral and antitumor IFN-γ and TNF-α. In chronic viral model, the numbers of antiviral effector and memory CD8+ T cells were decreased in IFNARfl/flxFoxp3YFP-Cre mice and the effector CD4+ and CD8+ T cells exhibited a phenotype compatible with enhanced exhaustion. IFNARfl/flxFoxp3YFP-Cre mice cleared Armstrong infection normally, but had higher viral titers in sera, kidneys and lungs during chronic infection, and higher tumor burden than the WT controls. The enhanced activated phenotype was evident through transcriptome analysis of IFNARfl/flxFoxp3YFP-Cre mice Tregs during infection demonstrated differential expression of a unique gene signature characterized by elevated levels of genes involved in suppression and decreased levels of genes mediating apoptosis. Thus, IFN signaling in Tregs is beneficial to host resulting in a more effective antiviral response and augmented antitumor immunity.