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Dendritic cells (DCs) are professional APCs of the immune system that continuously sample their environment and function to stimulate an adaptive immune response by initiating Ag-specific immunity or tolerance. Extracellular vesicles (EVs), small membrane-bound structures, are released from DCs and have been discovered to harbor functional peptide-MHC complexes, T cell costimulatory molecules, and other molecules essential for Ag presentation, immune cell regulation, and stimulating immune responses. As such, DC-derived EVs are being explored as potential immunotherapeutic agents. DC-derived EVs have also been implicated to function as a trafficking mechanism of infectious particles aiding viral propagation. This review will explore the unique features that enable DC-derived EVs to regulate immune responses and interact with recipient cells, their roles within Ag-presentation and disease settings, as well as speculating on a potential immunological role of apoptotic DC-derived EVs.

Sarcoidosis is a systemic inflammatory disease mainly affecting the lungs. The hallmark of sarcoidosis are granulomas that are surrounded by activated T cells, likely targeting the disease-inducing antigen. IFNγ-producing Th1 and Th17.1 T cells are elevated in sarcoidosis and associate with disease progression. Monocytes and dendritic cells (DCs) are antigen-presenting cells (APCs) and required for T cell activation. Several subsets of monocytes and DCs with different functions were identified in sarcoidosis. However, to what extent different monocyte and DC subsets can support activation and skewing of T cells in sarcoidosis is still unclear. In this study, we performed a transcriptional and functional side-by-side comparison of sorted monocytes and DCs from matched blood and bronchoalveolar lavage (BAL) fluid of sarcoidosis patients. Transcriptomic analysis of all subsets showed upregulation of genes related to T cell activation and antigen presentation in DCs compared with monocytes. Allogeneic T cell proliferation was higher after coculture with monocytes and DCs from blood compared with BAL and DCs induced more T cell proliferation compared with monocytes. After coculture, proliferating T cells showed high expression of the transcription factor Tbet and IFNγ production. We also identified Tbet and RORγt coexpressing T cells that mainly produced IFNγ. Our data show that DCs rather than monocytes from sarcoidosis patients have the ability to activate and polarize T cells towards Th1 and Th17.1 cells. This study provides a useful in vitro tool to better understand the contribution of monocytes and DCs to T cell activation and immunopathology in sarcoidosis.

Dendritic cells (DCs) are efficient antigen-presenting cells that serve as a link between the innate and adaptive immune systems. These cells are broadly involved in cellular and humoral immune responses by presenting antigens to initiate T cell reactions, cytokine and chemokine secretion, T cell differentiation and expansion, B cell activation and regulation, and the mediation of immune tolerance. The functions of DCs depend on their activation status, which is defined by the stages of maturation, phenotype differentiation, and migration ability, among other factors. IL-6 is a soluble mediator mainly produced by a variety of immune cells, including DCs, that exerts pleiotropic effects on immune and inflammatory responses through interaction with specific receptors expressed on the surface of target cells. Here, we review the role of IL-6, when generated in an inflammatory context or as derived from DCs, in modulating the biologic function and activation status of DCs and emphasize the importance of searching for novel strategies to target the IL-6/IL-6 signaling pathway as a means to diminish the inflammatory activity of DCs in immune response or to prime the immunogenic activity of DCs in immunosuppressive conditions.

T cell factor 1 (TCF-1) is a transcription factor (TF) of the canonical Wnt signaling pathway that encoded by the Tcf7. The crucial role of TCF-1 in T cell development and memory formation has been widely recognized. Recent studies have demonstrated that exhausted CD8+ T cell with the expression of TCF-1 may have inspiring function to amplify immunoreaction and improve the response to immunotherapy in chronic viral infection and cancer. In this short review, we summarized recent progress in intratumoral exhausted CD8+ T cells expressing TCF-1 that represent a fantastic subset with stem cell-like properties that associated with improved antitumor immunity and response to immune checkpoint blockade (ICB).

Communication between the nervous and immune systems serves a key role in host-protective immunity at mucosal barrier sites including the respiratory tract. In these tissues, neuroimmune interactions operate in bidirectional circuits that can sense and respond to mechanical, chemical, and biologic stimuli. Allergen- or helminth-induced products can produce airway inflammation by direct action on nociceptive afferents and adjacent tissues. The activity of nociceptive afferents can regulate innate and adaptive immune responses via neuropeptides and neurotransmitter signaling. This review will summarize recent work investigating the role of neuropeptides CGRP, VIP, neuromedins, substance P, and neurotransmitters dopamine and the B2-adrenoceptor agonists epinepherine/norepinepherine, each of which influence type 2 immunity by instructing mast cell, innate lymphoid cell type 2, dendritic cell, and T cell responses, both in the airway and the draining lymph node. Afferents in the airway also contain receptors for alarmins and cytokines, allowing their activity to be modulated by immune cell secreted products, particularly those secreted by mast cells. Taken together, we propose that further investigation of how immunoregulatory neuropeptides shape respiratory inflammation in experimental systems may reveal novel therapeutic targets for addressing the increasing prevalence of chronic airway disease in humans.

Obesity is an independent risk factor for morbidity and mortality in response to influenza infection. However, the underlying mechanisms by which obesity impairs immunity are unclear. Herein, we investigated the effects of diet-induced obesity on pulmonary CD8+ T cell metabolism, cytokine production, and transcriptome as a potential mechanism of impairment during influenza virus infection in mice. Male C57BL/6J lean and obese mice were infected with sub-lethal mouse-adapted A/PR/8/34 influenza virus, generating a pulmonary anti-viral and inflammatory response. Extracellular metabolic flux analyses revealed pulmonary CD8+ T cells from obese mice, compared with lean controls, had suppressed oxidative and glycolytic metabolism at day 10 post-infection. Flow cytometry showed the impairment in pulmonary CD8+ T cell metabolism with obesity was independent of changes in glucose or fatty acid uptake, but concomitant with decreased CD8+GrB+IFNγ+ populations. Notably, the percent of pulmonary effector CD8+GrB+IFNγ+ T cells at day 10 post-infection correlated positively with total CD8+ basal extracellular acidification rate and basal oxygen consumption rate. Finally, next-generation RNA sequencing revealed complex and unique transcriptional regulation of sorted effector pulmonary CD8+CD44+ T cells from obese mice compared to lean mice following influenza infection. Collectively, the data suggest diet-induced obesity increases influenza virus pathogenesis, in part, through CD8+ T cell-mediated metabolic reprogramming and impaired effector CD8+ T cell function.

IL-26 is a newly discovered IL-10 cytokine family member mainly secreted by Th17 cells. However, the relationship between IL-26 and lung cancer remains unclear. The present study reported that IL-26 is involved in the production and promotion of malignant pleural effusion (MPE) for the first time. The concentrations of IL-26 and several Th17-related cytokines in MPE and peripheral blood (PB) from MPE patients were measured. IL-26, IL-10, and IL-6 were elevated in MPE compared to PB. The cell resource of IL-26 was primary Th17 cells measured by flow cytometry, whereas Tc17 cells and macrophages could also contribute to higher concentration of IL-26 in MPE. Abundant IL-6 and IL-23 in MPE could promote the frequency of IL-26 expressed by CD4+ T cells through phosphorylating STAT3 signaling pathway and promoting the expression of a specific Th17 lineage marker RORγt subsequently. IL-26 could selectively increase Th22 proportion through up-regulating the percentage of Ki-67 expressed by CD4+ T cells and the expression of IL-22 secreted by memory CD4+ T cells. In addition, IL-26 could decrease secretion of granzyme B. The tumor-killing activity of CD8+ T cells were inhibited as well when cocultured with malignant cells. Furthermore, the accumulation of IL-26 protein in MPE predicted poor patient survival. In summary, our results indicated that IL-26 was involved in the pathogenesis of MPE by exerting its impacts on both CD4+ T cells and CD8+ T cells.

Preeclampsia, defined as new-onset hypertension accompanied by proteinuria occurring at 20 weeks of gestation or later, is a leading cause of perinatal morbidity and mortality worldwide. The pathophysiology of this major multi-systemic syndrome includes defective deep placentation, oxidative stress, endothelial dysfunction, the presence of an anti-angiogenic state, and intravascular inflammation, among others. In this review, we provide a comprehensive overview of the cellular immune responses involved in the pathogenesis of preeclampsia. Specifically, we summarize the role of innate and adaptive immune cells in the maternal circulation, reproductive tissues, and at the maternal-fetal interface of women affected by this pregnancy complication. The major cellular subsets involved in the pathogenesis of preeclampsia are regulatory T cells, effector T cells, NK cells, monocytes, macrophages, and neutrophils. We also summarize the literature on those immune cells that have been less characterized in this clinical condition, such as γδ T cells, invariant natural killer T cells, dendritic cells, mast cells, and B cells. Moreover, we discuss in vivo studies utilizing a variety of animal models of preeclampsia to further support the role of immune cells in this disease. Finally, we highlight the existing gaps in knowledge of the immunobiology of preeclampsia that require further investigation. The goal of this review is to promote translational research leading to clinically relevant strategies that can improve adverse perinatal outcomes resulting from the obstetrical syndrome of preeclampsia.

Tissue-resident γδ T cells form the first line of defense at barrier surfaces where they survey host tissue for signs of stress or damage. Following recognition of injury, γδ T cells play a crucial role in the wound-healing response through the production of growth factors and cytokines that promote proliferation in surrounding epithelial cells. To initiate this response, γδ T cells require interactions with a variety of epithelial-expressed costimulatory molecules in addition to primary signaling through their TCR. In the epidermis these signals include the coxsackie and adenovirus receptor (CAR), histocompatibility antigen 60c (H60c), and plexin B2, which interact with γδ T cell-expressed junctional adhesion molecule-like protein (JAML), NKG2D, and CD100, respectively. Here we identify heat shock protein family A member 8 (Hspa8) and ICAM-1 as two additional keratinocyte-expressed costimulatory molecules for epidermal resident γδ T cells (termed DETC). These molecules were rapidly up-regulated in the epidermis following wounding in both mouse and human tissue. Both Hspa8 and ICAM-1 had a costimulatory effect on DETC, inducing proliferation, CD25 up-regulation, and IL-2 production. We also provide evidence that DETC can be activated through the potential ICAM-1 and Hspa8 receptors LFA-1 and CD316. Finally, knockdown of Hspa8 in keratinocytes reduced their ability to activate DETC in culture and ICAM-1−/− mice exhibited impaired rates of healing in skin-organ culture suggesting a role for these proteins in the DETC-mediated damage response. Together with previous work on CAR, H60c, and plexin B2, these results add to a picture of a complex keratinocyte wound signature that is required for efficient DETC activation.

Fas ligand (FasL) is best known for its ability to induce cell death in a wide range of Fas-expressing targets and to limit inflammation in immunoprivileged sites such as the eye. In addition, the ability of FasL to induce a much more extensive list of outcomes is being increasingly explored and accepted. These outcomes include the induction of proinflammatory cytokine production, T cell activation, and cell motility. However, the distinct and opposing functions of membrane-associated FasL (mFasL) and the C-terminal soluble FasL fragment (sFasL) released by metalloproteinase cleavage is less well documented and understood. Both mFasL and sFasL can form trimers that engage the trimeric Fas receptor, but only mFasL can form a multimeric complex in lipid rafts to trigger apoptosis and inflammation. By contrast, a number of reports have now documented the anti-apoptotic and anti-inflammatory activity of sFasL, pointing to a critical regulatory function of the soluble molecule. The immunomodulatory activity of FasL is particularly evident in ocular pathology where elimination of the metalloproteinase cleavage site and the ensuing increased expression of mFasL can severely exacerbate the extent of inflammation and cell death. By contrast, both homeostatic and increased expression of sFasL can limit inflammation and cell death. The mechanism(s) responsible for the protective activity of sFasL are discussed but remain controversial. Nevertheless, it will be important to consider therapeutic applications of sFasL for the treatment of ocular diseases such as glaucoma.

Immunity is governed by successful T cell migration, optimized to enable a T cell to fully scan its environment without wasted movement by balancing speed and turning. Here we report that the Arhgef6 RhoGEF (aka alpha-PIX; αPIX; Cool-2), an activator of small GTPases, is required to restrain cell migration speed and cell turning during spontaneous migration on 2D surfaces. In Arhgef6−/− T cells, expression of Arhgef7 (beta-PIX; βPIX; Cool-1), a homolog of Arhgef6, was increased and correlated with defective activation and localization of Rac1 and CDC42 GTPases, respectively. Downstream of Arhgef6, PAK2 (p21-activated kinase 2) and LIMK1 phosphorylation was reduced, leading to increased activation of Cofilin, the actin-severing factor. Consistent with defects in these signaling pathways, Arhgef6−/− T cells displayed abnormal bilobed lamellipodia and migrated faster, turned more, and arrested less than wild-type (WT) T cells. Using pharmacologic inhibition of LIMK1 (LIM domain kinase 1) to induce Cofilin activation in WT T cells, we observed increased migration speed but not increased cell turning. In contrast, inhibition of Cdc42 increased cell turning but not speed. These results suggested that the increased speed of the Arhgef6−/− T cells is due to hyperactive Cofilin while the increased turning may be due to abnormal GTPase activation and recruitment. Together, these findings reveal that Arhgef6 acts as a repressor of T cell speed and turning by limiting actin polymerization and lamellipodia formation.

The immune system plays a crucial role in the response against severe acute respiratory syndrome coronavirus 2 with significant differences among patients. The study investigated the relationships between lymphocyte subsets, cytokines, and disease outcomes in patients with coronavirus disease 2019 (COVID‐19). The measurements of peripheral blood lymphocytes subsets and cytokine levels were performed by flow cytometry for 57 COVID‐19 patients. Patients were categorized into two groups according to the severity of the disease (nonsevere vs. severe). Total lymphocytes, T cells, CD4+ T cells, CD8+ T cells, B cells, and natural killer cells were decreased in COVID‐19 patients and statistical differences were found among different severity of illness and survival states (P ˂ 0.01). The levels of IL‐6 and IL‐10 were significantly higher in severe and death groups and negatively correlated with lymphocyte subsets counts. The percentages of Th17 in the peripheral blood of patients were higher than those of healthy controls whereas the percentages of Th2 were lower. For the severe cases, the area under receiver operating characteristic (ROC) curve of IL‐6 was the largest among all the immune parameters (0.964; 95% confidence interval: 0.927–1.000, P 106.44 pg/ml and CD8+ T cell counts, Graphical Abstract COVID‐19 patients with poor prognosis exhibited a significant depletion of lymphocyte‐subset counts, with remarkably increasing concentrations of IL6 and IL10.

The role of Myeloid-Derived Suppressor Cells (MDSC) in infant immune ontogeny is unknown. Here, we evaluated MDSC frequency and relationship with infant vaccine responses throughout the first year of life in a prospective cohort study. Ninety-one South African infant-mother pairs were enrolled at delivery, and blood samples were collected at 0, 6, 10, and 14 weeks, 6 months, 9 months, and 1 year. MDSC frequencies were quantified, and immune responses to the childhood vaccines Bacillus Calmette-Guérin (BCG), hepatitis B (HepB), and combination diphtheria, tetanus, and pertussis (dTaP) were measured by Ag-specific CD4+ T cell proliferation and interferon gamma (IFN-γ) production. Vaccine-specific Ab responses to HepB, dTaP, and Haemophilus influenzae type b (Hib) were quantified via Enzyme-Linked Immunosorbent assay (ELISA). MDSC frequency in mother-infant pairs was strongly correlated; the frequency of MDSC decreased in both mothers and infants during the months after delivery/birth; and by 1 year, infant MDSC frequencies rebounded to birth levels. Higher MDSC frequency at vaccination was associated with a lack of subsequent IFN-γ release in response to vaccine Ags, with the exception of BCG. With the exception of a weak, positive correlation between MDSC frequency at 6 weeks (time of initial vaccination) and peak Hepatitis B surface antigen Ab titer, Polymorphonuclear Myeloid-Derived Suppressor Cells (PMN-MDSC) was not correlated with T cell proliferation or Ab responses in this study. The potential for MDSC-mediated suppression of vaccine Ag-specific IFN-γ responses should be explored further, and considered when evaluating candidate infant vaccines.

Clostridioides difficile (C. difficile) is the major cause of hospital-acquired gastrointestinal infections in individuals following antibiotics treatment. The pathogenesis of C. difficile infection (CDI) is mediated mainly by the production of toxins that induce tissue damage and host inflammatory responses. While innate immunity is well characterized in human and animal models of CDI, adaptive immune responses remain poorly understood. In this review, the current understanding of adaptive immunity is summarized and its influence on pathogenesis and disease outcome is discussed. The perspectives on what we believe to be the main pending questions and the focus of future research are also provided. There is no doubt that the innate immune response provides a first line of defense to CDI. But, is the adaptive immune response a friend or a foe? Probably it depends on the course of the disease. Adaptive immunity is essential for pathogen eradication, but may also trigger uncontrolled or pathological inflammation. Most of the understanding of the role of T cells is based on findings from experimental models. While they are a very valuable tool for research studies, more studies in human are needed to translate these findings into human disease. Another main challenge is to unravel the role of the different T cell populations on protection or induction of immunopathogenesis.

A defining feature of protracted sepsis is development of immunosuppression that is thought to be a major driving force in the morbidity and mortality associated with the syndrome. The immunosuppression that occurs in sepsis is characterized by profound apoptosis-induced depletion of CD4 and CD8 T cells and severely impaired T cell function. OX40, a member of the TNF receptor superfamily, is a positive co-stimulatory molecule expressed on activated T cells. When engaged by OX40 ligand, OX40 stimulates T cell proliferation and shifts the cellular immune phenotype toward TH1 with increased production of cytokines that are essential for control of invading pathogens. The purpose of the present study was to determine if administration of agonistic Ab to OX40 could reverse sepsis-induced immunosuppression, restore T cell function, and improve survival in a clinically relevant animal model of sepsis. The present study demonstrates that OX40 agonistic Ab reversed sepsis-induced impairment of T cell function, increased T cell IFN-γ production, increased the number of immune effector cells, and improved survival in the mouse cecal ligation and puncture model of sepsis. Importantly, OX40 agonistic Ab was not only effective in murine sepsis but also improved T effector cell function in PBMCs from patients with sepsis. The present results provide support for the use of immune adjuvants that target T cell depletion and T cell dysfunction in the therapy of sepsis-induced immunosuppression. In addition to the checkpoint inhibitors anti-PD-1 and anti-PD-L1, OX40 agonistic Ab may be a new therapeutic approach to the treatment of this highly lethal disorder.

Hepatitis B virus (HBV)-specific T cells play a critical role in determining the outcome of HBV infection. However, T cell response induced by predominant Ag in chronic infection is hardly detectable owing to the lack of a suitable assay. We herein established an optimized method to enumerate HBV-specific T cells and assessed the association between HBV surface Ag (HBsAg) and HBV DNA. Sixty chronic HBV infection patients were enrolled. HBV-specific T cells were expanded by using overlapping peptide pools covering the entire sequence of HBV genotypes B and C. IFN-γ-producing HBV-specific T cells were detected by a cultured enzyme-linked immunospot (ELISPOT) assay, ex vivo ELISPOT assay, or flow cytometry staining. The association between HBV-specific T cells and serum levels of HBsAg and HBV DNA were analyzed. Cultured ELISPOT assay had a higher sensitivity than ex vivo ELISPOT in the detection of HBV-specific T cells. Moreover, consistent results were acquired by flow cytometry analysis and cultured ELISPOT assay, but the latter required only a limited number of cells for detection. Interestingly, HBV core peptide pool induced a robust HBV-specific T cell response in patients with lower levels of HBV DNA and HBsAg. Specifically, the frequency of HBV core Ag-specific IFN-γ+ spot-forming cells was inversely correlated with serum levels of HBV DNA and HBsAg. An optimized cultured ELISPOT assay reveals the association between HBV core Ag-induced T cell response and HBV control; this method may favor the investigation of HBV-specific T cell in chronic HBV infection.

Asthma is one of the most common chronic and inflammatory respiratory diseases, which is estimated to affect 1–10% of the population in different regions across the world. Previous studies have shown that recombinant Ling-Zhi 8 (rLZ-8), an immunoregulatory protein originally extracted from Ganoderma lucidum, plays multiple roles in regulating murine immune cells, including T cells. Here, we examined whether rLZ-8 would ameliorate pulmonary inflammation in a model of asthma-like mice. We found that rLZ-8 significantly inhibited the lung inflammation and reduced infiltration of inflammatory cells, including dendritic cells and eosinophils, in OVA-induced asthmatic mice. It also deceased IL-17A level but increased IL-10 level in bronchoalveolar lavage fluid (BALF) while reducing RORγt mRNA expression and enhancing Foxp3 mRNA level in the lung tissue. Flow cytometry studies demonstrated that rLZ-8 remarkably down-regulated Th17 cells but upregulated Foxp3+ regulatory T (Treg) cells, rather than influencing Th1 versus Th2 cells. Experiments in vitro also showed that rLZ-8 suppressed murine CD3+ T cell proliferation and reduced the frequency of Th17 cells while promoting the differentiation of CD4+Foxp3+ Tregs. Moreover, rIL-8 similarly altered human Th17/Treg generation or their balance in vitro. Finally, we found that rLZ-8 suppressed signaling pathways of both STAT3 and NF-κB (P100/P52) in murine lung tissue as well as cultured T cells. Thus, we have demonstrated that rLZ-8 attenuates pulmonary inflammation through regulating the balance of Th17/Treg cells in OVA-induced asthmatic mice and that rLZ-8 may be a potential therapeutic agent for the treatment of asthma in clinic.

Artemisinin (ART) has been shown to suppress B cell activation and plasma cell formation. However, its effect on splenic marginal zone (MZ) B cells is unknown. Splenic MZ B cells play a critical role in rapidly induced Ab production against blood-borne foreign Ags. Dysfunction of MZ B cells, due to inhibition of its proliferation or displacement of its homing, results in an attenuated adaptive humoral response. Here, we investigate the effect of ART on splenic MZ B (CD19+CD21highCD23low) and B10 (CD19+CD1dhighCD5+) B cells to explore the mechanisms of ART-induced immunosuppression in T cell-deficient nude mice challenged with hamster xenoantigens. In this study, we demonstrate that ART decreases T cell-independent xenogeneic IgM Ab production and, this is associated with a strong suppression of MZ B cell proliferation and a relative increase of CD21lowCD23+ follicular and B10 B cells. In addition, this suppression impairs IL-10 production. Taken together, our data indicate that ART suppresses B cell immune responses through a distinctive effect on splenic MZ B and other B cells. This represents a new mechanism of ART-induced immunosuppression.

CD4+ regulatory T cells (Tregs) are acutely activated by traumatic injury, which suggests that they may react to injury with similar kinetics as memory T cells. Here, we used a mouse burn trauma model to screen for memory-like T cell responses to injury by transferring T cells from sham or burn CD45.1 mice into CD45.2 mice and performing secondary injuries in recipient mice. Among all T cell subsets that were measured, only Tregs expanded in response to secondary injury. The expanded Tregs were a CD44high/CD62Llow subpopulation, markers indicative of memory T cells. CyTOF (cytometry by time-of-flight) mass cytometry was used to demonstrate that injury-expanded Tregs expressed higher levels of CD44, CTLA-4, ICOS, GITR, and Helios than Tregs from noninjured mice. Next, we tested whether a similar population of Tregs might react acutely to burn trauma. We observed that Tregs with a phenotype that matched the injury-expanded Tregs were activated by 6 h after injury. To test if Treg activation by trauma requires functional MHC class II, we measured trauma-induced Treg activation in MHC class II gene deficient (MHCII−/−) mice or in mice that were given Fab fragment of anti-MHC class II antibody to block TCR activation. Injury-induced Treg activation occurred in normal mice but only partial activation was detected in MHCII−/− mice or in mice that were given Fab anti-MHCII antibody. These findings demonstrate that trauma activates a memory-like Treg subpopulation and that Treg activation by injury is partially dependent on TCR signaling by an MHC class II dependent mechanism.

IFN-γ-producing γδ T cells have been suggested to play an important role in protection against infection with Trypanosoma cruzi. However, little is known about the mechanisms leading to functional differentiation of this T cell subset in this model. In the current work, we investigated the possibility that the IL-18/MyD88 pathway is central for the generation of effector γδ T cells, playing a role for resistance against infection. We found that splenic γδ+CD3+ cells were rapidly expanded (10–14 days post infection), which was accompanied by an early γδ T cell infiltration into the heart. In the following days, intracardiac parasitism was reduced, the protective immunity being accompanied by decreased γδ T cells tissue infiltration. As predicted, there was a drastic reduction of γδ T cells in Myd88- and Il18r1-deficient mice, both transgenic strains displaying a susceptible phenotype with increased intracardiac parasitism. In vivo and in vitro assays confirmed that IL-18R deficiency hampered γδ T cell proliferation. Further characterization revealed that T. cruzi infection up-regulates IL-18R expression in WT γδ+ T cell population whereas Il18r1−/− mice showed impaired generation of cytotoxic GzB+ and IFN-γ-producing γδ T cells. Consistently, in vitro cytotoxicity assay confirmed that cytolytic function was impaired in Il18r1-deficient γδ T cells. As a proof of concept, adoptive transfer of WT γδ T cells rescues Il18r1-deficient mice from susceptibility, reducing parasitemia and abrogating the mortality. Collectively, our findings implicate the IL-18R-MyD88 signaling in the mechanisms underlying generation of immunoprotective γδ T cells response in experimental Trypanosoma cruzi infection.

The immunosuppressive properties of vascular endothelial growth factors (VEGFs) suggest a new role of angiogenic factors in T cell modulation in cancer and pregnancy. Most of VEGF effects on T cells are mediated through the VEGF receptor type 2 (VEGFR-2). This study aims to investigate the role of placental growth factor (PlGF) as a selective VEGFR-1 ligand in the modulation of human T cells functions. For this, PBMCs from healthy donors were stimulated with anti-CD3 mAbs (a-CD3) or Concanavalin A (ConA) in the absence or presence of PlGF and assessed for T cell proliferation, IL-10 production, programmed cell death, and the expression of inhibitory receptors (PD-1, CTLA-4, TIM-3) using radiometric (3H-thymidine incorporation) and FACS analysis. We showed that most T cells in freshly isolated PBMCs lacked VEGFR-1. However, activation with a-CD3 or ConA strongly increased the percentages of VEGFR-1 expressing CD4+ and CD8+ T cells. PlGF in a wide dose range suppressed PBMC cell proliferation, inhibiting both CD4+ and CD8+ T cells. Blockade of VEGFR-1, but not VEGFR-2 with neutralizing Abs completely abolished the suppressive effect of PlGF. Furthermore, we found that treatment with PlGF up-regulated IL-10 production in CD4+ and CD8+ T cells, promoted CD8+ T cells apoptosis and enhanced the expression of inhibitory receptors (PD-1 and TIM-3) on activated T cells. Our in vitro findings suggest the involvement of PlGF/VEGFR-1 signaling in the modulation of T cell responses in a-CD3-stimulated PBMCs.

Tissue resident memory T cells (Trm) are critical for local protection against reinfection. The accumulation of T cells in the tissues requires a post-priming signal from TNFR superfamily members, referred to as signal 4. Glucocorticoid-induced TNFR-related protein (GITR; TNFRSF18) signaling is important for this post-priming signal and for Trm formation during respiratory infection with influenza virus. As GITR signaling impacts both effector T cell accumulation and Trm formation, we asked if GITR differentially affects subsets of effector cells with different memory potential. Effector CD4+ T cells can be subdivided into 2 populations based on expression of lymphocyte antigen 6C (Ly6C), whereas effector CD8+ cells can be divided into 3 populations based on Ly6C and CX3CR1. The Ly6Chi and CX3CR1hi T cell populations represent the most differentiated effector T cells. Upon transfer, the Ly6Clo CD4+ effector T cells preferentially enter the lung parenchyma, compared to the Ly6Chi CD4+ T cells. We show that GITR had a similar effect on the accumulation of both the Ly6Chi and Ly6Clo CD4+ T cell subsets. In contrast, whereas GITR increased the accumulation of all three CD8+ T cell subsets defined by CX3CR1 and Ly6C expression, it had a more substantial effect on the least differentiated Ly6Clo CX3CR1lo subset. Moreover, GITR selectively up-regulated CXCR6 on the less differentiated CX3CR1lo CD8+ T cell subsets and induced a small but significant increase in CD127 selectively on the Ly6Clo CD4+ T cell subset. Thus, GITR contributes to accumulation of both differentiated effector cells as well as memory precursors, but with some differences between subsets.

Adipose tissue-resident F4/80hi macrophages (ATMs) are the main leukocyte population found in the visceral adipose tissue (VAT). These macrophages comprise several phenotypically distinct subpopulations that rapidly shift in abundance during obesity-induced tissue remodeling. Here we used a fate-mapping approach in mouse models to determine the developmental origins and the differential turnover kinetics of ATMs in lean and obese adipose tissue. We found that in lean, murine VAT the majority of ATMs express T cell immunoglobulin and mucin domain containing 4 receptor (Tim-4), lack the expression of CCR2 and can be further subdivided based on their expression of MHC class II and CD11c. We showed that both embryonic-derived Tim-4+ MHCIIlow and Tim-4+ MHCII+ ATM subsets are long-lived and only slowly replenished by monocytes over time. Only a minor Tim-4- MHCII+ CD11c+ ATM fraction expresses CCR2 and is short-lived. In response to high-fat induced VAT remodeling, the majority of Tim-4+ MHCIIlow ATMs maintain their fetal identity as they are moderately displaced by monocytes. Conversely, Tim-4+ MHCII+ ATMs are quickly replaced in a CCR2-dependent manner by bone marrow-derived Tim-4- MHCII+ ATMs that have significantly higher turnover rates than those in lean mice. In addition, during high-fat diet, the subpopulation of CD11c+ macrophages invade the VAT with the fastest turnover kinetics of all three ATM subpopulations. Our results suggest that ATM subpopulation frequency is controlled by the VAT microenvironment and that obesity-induced tissue remodeling renders some of the ATM niches accessible and available for rapid monocyte replenishment. Specialized monocyte-derived macrophages, which are rapidly recruited may be contributing to control the excess of adipocyte-released lipids produced during obesity. Ministry of Education (MOE) This work was supported by Ministry of Education Tier2 grants awarded to C.R. (grant numbers: MOE2016-T2-1-012 and MOE2018-T2-2-016)

Glucocorticoid-induced tumor necrosis factor receptor family-related protein ligand (GITRL), a member of the tumor necrosis factor superfamily, is expressed in APCs and acts as a costimulatory molecule in the immune system. Although the glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR)/GITRL system has been modulated to promote or decrease T cell-related responses in multiple diseases, studies in macrophages are limited. To address this issue, we compared the expression of GITRL in various types of macrophages and analyzed whether GITRL can affect the fundamental properties and major functions of these cells. Our results demonstrated that M1 polarized macrophages had the highest GITRL levels. Furthermore, GITRL overexpression skewed macrophage polarization toward the M1 phenotype, accelerating proliferation and migration and regulating phagocytosis and killing function. Moreover, GITRL-silenced cells showed a loss of these functions, further confirming its vital role. We also developed an acute peritonitis mouse model, in which macrophages were driven to differentiate into a proinflammatory phenotype with GITRL up-regulation, triggering a positive feedback loop. Our results provide molecular insight into how the GITR/GITRL system modulates innate immune responses, suggesting that manipulation of the GITR/GITRL system to treat diseases depends not only on T cell regulation but also on macrophage participation.

Epithelial ovarian cancer displays the highest mortality of all gynecological tumors. A relapse of the disease even after successful surgical treatment is a significant problem. Resistance against the current platinum‐based chemotherapeutic standard regime requires a detailed ex vivo immune profiling of tumor‐infiltrating cells and the development of new therapeutic strategies. In this study, we phenotypically and functionally characterize tumor cells and autologous tumor‐derived αβ and γδ T lymphocyte subsets. Tumor‐infiltrating (TIL) and tumor‐ascites lymphocytes (TAL) were ex vivo isolated out of tumor tissue and ascites, respectively, from high‐grade ovarian carcinoma patients (FIGO‐stage IIIa‐IV). We observed an increased γδ T cell percentage in ascites compared to tumor‐tissue and blood of these patients, whereas CD8+ αβ T cells were increased within TAL and TIL. The number of Vδ1 and non‐Vδ1/Vδ2‐expressing γδ T cells was increased in the ascites and in the tumor tissue compared to the blood of the same donors. Commonly in PBL, the Vγ9 chain of the γδ T cell receptor is usually associated exclusively with the Vδ2 chain. Interestingly, we detected Vδ1 and non‐Vδ1/Vδ2 T cells co‐expressing Vγ9, which is so far not described for TAL and TIL. Importantly, our data demonstrated an expression of human epidermal growth factor receptor (HER)‐2 on high‐grade ovarian tumors, which can serve as an efficient tumor antigen to target CD3 TIL or selectively Vγ9‐expressing γδ T cells by bispecific antibodies (bsAbs) to ovarian cancer cells. Our bsAbs efficiently enhance cytotoxicity of TIL and TAL against autologous HER‐2‐expressing ovarian cells., Tumor‐infiltrating γδ T cells are attractive effector cells for targeting with bispecific antibodies in the treatment of ovarian cancer cells.

IDO is an enzyme that participates in the degradation of tryptophan (Trp), which is an essential amino acid necessary for vital cellular processes. The degradation of Trp and the metabolites generated by the enzymatic activity of IDO can have immunomodulating effects, notably over T cells, which are particularly sensitive to the absence of Trp and leads to the inhibition of T cell activation, cell death, and the suppression of T cell effector functions. Noteworthy, T cells participate in the cellular immune response against the human respiratory syncytial virus (hRSV) and are essential for viral clearance, as well as the total recovery of the host. Furthermore, inadequate or non‐optimal polarization of T cells is often seen during the acute phase of the disease caused by this pathogen. Here, we discuss the capacity of hRSV to exploit the immunosuppressive features of IDO to reduce T cell function, thus acquiring relevant aspects during the biology of the virus. Additionally, we review studies on the influence of IDO over T cell activation and its relationship with hRSV infection., Review of the capacity of hRSV to exploit the immunosuppressive features of IDO to reduce T cell function and activation.

Cytoskeletal reorganization driven by Rho GTPases plays a crucial role in the migration of T cells, which are key regulators of immunity. The molecular mechanisms that control actin cytoskeleton remodeling during T cell movement have only partially been clarified as the function of many modulators has not been evaluated in these cells. Here, we report a new function of RhoGDI2 by showing that this protein positively regulates Rho GTPase activation during T cell adhesion and migration. RhoGDI2 knockdown significantly reduced T cell adhesion and migration. Furthermore, RhoGDI2 knockdown decreased the activation of Rac1 and Cdc42, 2 members of Rho GTPases, and the remodeling of the actin cytoskeleton. Upon P-selectin glycoprotein ligand-1 engagement, RhoGDI2 was phosphorylated at Y24 and Y153 by kinases related to β2 integrin outside-in signaling, Src, c-Abl, and Syk, resulting in the accumulation of RhoGDI2 at the cell membrane. Subsequent phosphorylation of S31 induced the opening of RhoGDI2 and the release of Rho GTPases, whereas phosphorylation of Y153 might promote the activation of Rho GTPases by recruiting Vav1. Moreover, the disruption of lipid rafts with methyl-β-cyclodextrin blocked the interaction between integrins and RhoGDI2, reducing the level of phosphorylated RhoGDI2 and the activation of downstream Rho GTPases. Based on these observations, RhoGDI2 is a target of intergrin outside-in signaling that activates Rho GTPases during T cell adhesion and migration, and RhoGDI2-mediated signal transduction is based on the lipid rafts integrity.

CXCL17 is a homeostatic chemokine in the mucosa known to chemoattract dendritic cells and macrophages but can also be expressed elsewhere under inflammatory conditions. Cxcl17−/− mice have lower numbers of macrophages or dendritic cells in mucosal tissues. CXCL17 is also able to chemoattract suppressor myeloid cells that can recruit regulatory T cells. To explore a possible role of Cxcl17 in T cells, we studied T cell populations from Cxcl17−/− or wild-type (WT) littermate mice. Cxcl17−/− mice have higher numbers of CD4+ and CD8+ T cells in spleen and lymph nodes (LNs). Upon activation, they produce higher levels of several proinflammatory cytokines and chemokines. Furthermore, a Cxcl17−/− mouse developed exacerbated disease in a T cell-dependent model of experimental autoimmune encephalomyelitis (EAE). By 18 days after immunization with myelin oligodendrocyte peptide, only 44% of Cxcl17−/− mice were still alive vs. 90% for WT mice. During EAE, Cxcl17−/− mice exhibited higher numbers of lymphoid and myeloid cells in spleen and LNs, whereas they had less myeloid cell infiltration in the CNS. Cxcl17−/− mice also had higher levels of some inflammatory cytokines in serum, suggesting that they may be involved in the poor survival of these mice. Abnormal T cell function may reflect altered myeloid cell migration, or it could be due to altered T cell development in the thymus. We conclude that CXCL17 is a novel factor regulating T cell homeostasis and function.

Cervical cancer continues to be a public health problem in developing countries. Previous studies have shown that cervical cancer cells display markers of aerobic glycolysis, indicating that these tumors are likely to secrete lactate. Mostly, lactate is recognized as a molecule capable of suppressing immune responses, through inhibition of T cells, Mϕs, and dendritic cells. We and others have previously shown that Mϕs are frequent cells infiltrating cervical cancers with the ability to inhibit antitumor immune responses and promote tumor growth through angiogenesis. Here, we have tested the hypothesis that lactate, secreted by cervical cancer cells, can modulate Mϕ phenotype. First, we showed higher lactate plasma concentrations in patients with increasing cervical lesion grades, with maximum concentration in the plasma of cancer patients, which supported our hypothesis. We then inhibited lactate production in tumor cell spheroids established from cervical cancer derived cell lines, using the lactate dehydrogenase inhibitor, oxamate, prior to co-culture with monocytes. Lactate mediated part of the crosstalk between tumor cells and Mϕs, promoting secretion of IL-1β, IL-10, IL-6, and up-regulation of hypoxia induced factor-1α expression, and down-regulation of p65-NFκB phosphorylation in Mϕs. We also showed that Mϕs from co-cultures treated with oxamate were better inducers of T cell activation. Of note, experiments performed with inhibition of the monocarboxylate transporters rendered similar results. Our data confirms the hypothesis that lactate, secreted by cervical tumor cells, influences the phenotype of tumor Mϕs, promoting a suppressive phenotype.

Myeloid-derived suppressor cells (MDSCs) are a diverse group of cells that are recognized for their remarkable suppressive effects on pro-inflammatory T cells. The pleiotropic nature of these cells, however, has been demonstrated by their differential effects on immune responses in different settings. Our and others’ work has demonstrated suppressive effects of these cells. We previously demonstrated that these cells were mobilized to the lungs during experimental autoimmune encephalomyelitis (EAE), which is a murine model of multiple sclerosis, and potently inhibited CD8+ T cell responses against influenza infection. Interestingly, they appeared to have a lesser effect on CD4+ T cells, and in fact, others have demonstrated that spleen-derived MDSCs could actually promote Th17 differentiation. We sought to determine the role of lung-derived MDSCs on EAE pathogenesis, as excursion through the lungs by pathologic CNS-Ag targeted T cells was shown to be critical for EAE induction. Our results indicate a robust accumulation of granulocytic MDSCs in the lungs of mice during EAE, which could promote Th17 polarization, and which coincided with the trafficking of autoimmune-targeted T cells through the lungs. These studies underscore the pleiotropic effect of MDSCs on T cells and their potential pro-inflammatory phenotypes in neuro-inflammatory disease. Understanding both the intrinsic multifunctional nature of these cells and the ability to influence organ-specific targets such as the CNS from remote organs such as lungs will help to elucidate both mechanisms of disease and possible new therapeutic approaches.