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Previous work has shown that Secretory-IgA (SIgA) binding to the intestinal microbiota is variable and may regulate host inflammatory bowel responses. Nevertheless, the impact of the SIgA functional binding to the microbiota remains largely unknown in preterm infants whose immature epithelial barriers make them particularly susceptible to inflammation. Here, we investigated SIgA binding to intestinal microbiota isolated from stools of preterm infants

Objectives Francisella tularensis, the causative agent of tularaemia, is an exceptionally infectious bacterium, potentially fatal for humans if left untreated and with the potential to be developed as a bioweapon. Both natural infection and live‐attenuated vaccine strain (LVS) confer good protection against tularaemia. LVS vaccination is traditionally administered by scarification, and the formation of a cutaneous reaction or take at the vaccination site is recognised as a clinical correlate of protection. Although previous studies have suggested that high antibody titres following vaccination might serve as a useful surrogate marker, the immunological correlates of protection remain unknown. Methods We investigated the host T‐cell‐mediated immune (T‐CMI) responses elicited following immunisation with LVS vaccine formulated by the DynPort Vaccine Company (DVC‐LVS) or the United States Army Medical Research Institute of Infectious Diseases (USAMRIID‐LVS). We compared T‐CMI responses prompted by these vaccines and correlated them with take size. Results We found that both LVS vaccines elicited similar T‐CMI responses. Interestingly, take size associated with the T cells’ ability to proliferate, secrete IFN‐γ and mobilise degranulation, suggesting that these responses play an essential role in tularaemia protection. Conclusions These results renew the appreciation for vaccination through the scarification as a prime route of inoculation to target pathogens driving specific T‐CMI responses and provide further evidence that T‐CMI plays a role in protection from tularaemia., The actual immunological correlate(s) of protection from tularaemia in humans remain(s) unknown. As with smallpox, take is widely accepted as a clinical correlate of protection against tularaemia. We report, for the first time, a correlation between take‐lesion size and cellular‐mediated immune responses in humans after tularaemia immunization.

Enteric fevers, caused by the Salmonella enterica serovars Typhi (ST), Paratyphi A (PA) and Paratyphi B (PB), are life-threatening illnesses exhibiting very similar clinical symptoms but with distinct epidemiologies, geographical distributions and susceptibilities to antimicrobial treatment. Nevertheless, the mechanisms by which the host recognizes pathogens with high levels of homology, such as these bacterial serovars, remain poorly understood. Using a three-dimensional organotypic model of the human intestinal mucosa and PA, PB, and ST, we observed significant differences in the secretion patterns of pro-inflammatory cytokines and chemokines elicited by these serovars. These cytokines/chemokines were likely to be co-regulated and influenced the function of epithelial cells, such as the production of IL-8. We also found differing levels of polymorphonuclear leukocyte (PMN) migration among various infection conditions that either included or excluded lymphocytes and macrophages (Mϕ), strongly suggesting feedback mechanisms among these cells. Blocking experiments showed that IL-1β, IL-6, IL-8, TNF-α and CCL3 cytokines were involved in the differential regulation of migration patterns. We conclude that the crosstalk among the lymphocytes, Mϕ, PMN and epithelial cells is cytokine/chemokine-dependent and bacterial-serotype specific, and plays a pivotal role in orchestrating the functional efficiency of the innate cells and migratory characteristics of the leukocytes., Author summary Enteric fevers are acute illnesses caused mainly by the Salmonella enterica serovars Typhi (ST), Paratyphi A (PA) and Paratyphi B (PB). The incidence of enteric fevers is very low in industrialized countries, with most infections occurring in military personnel and individuals traveling to endemic areas. Nevertheless, worldwide, more than 20.6 million cases of enteric fever occur annually in low- and middle-income countries and are associated with approximately 129,000–223,000 deaths. ST, PA, and PB exhibit very similar clinical symptoms but distinct epidemiologies, geographical distributions, and susceptibilities to antimicrobial treatment. However, the mechanisms by which the host recognizes pathogens with high levels of homology, such as these bacterial serovars, remain poorly understood. Using an in vitro model of the human intestinal mucosa, we found that the crosstalk among leukocytes—lymphocytes, Mϕ, and PMN- and epithelial cells is cytokine/chemokine-dependent, and bacterial-serotype specific and plays a pivotal role in orchestrating the functional efficiency of the innate cells and migratory characteristics of the leukocytes.

Summary Secretory immunoglobulin A (SIgA) antibodies play an important role in protecting the mucosal surfaces against pathogens and maintaining homeostasis with the commensal microbiota. Because a substantial portion of the gut microbiota is coated with SIgA, we hypothesized that microbiota–SIgA complexes are important for the maintenance of gut homeostasis. Here we investigated the relationship between microbiota–SIgA complexes and inflammatory epithelial cell responses. We used a multi-cellular three-dimensional (3D) organotypical model of the human intestinal mucosa composed of an intestinal epithelial cell line and primary human lymphocytes/monocytes, endothelial cells and fibroblasts. We also used human SIgA from human colostrum, and a prominent bacterial member of the first colonizers, Escherichia coli, as a surrogate commensal. We found that free and microbiota-complexed SIgA triggered different epithelial responses. While free SIgA up-regulated mucus production, expression of polymeric immunoglobulin receptor (pIgR) and secretion of interleukin-8 and tumoir necrosis factor-α, microbiota-complexed SIgA mitigated these responses. These results suggest that free and complexed SIgA have different functions as immunoregulatory agents in the gut and that an imbalance between the two may affect gut homeostasis.

A notable proportion of Salmonella-associated gastroenteritis in the United States is attributed to Salmonella enterica serovar Typhimurium. We have previously shown that live-attenuated S. Typhimurium vaccine candidate CVD 1921 (I77 ΔguaBA ΔclpP) was safe and immunogenic in rhesus macaques but was shed for an undesirably long time postimmunization. In mice, occasional mortality postvaccination was also noted (approximately 1 in every 15 mice). Here we describe a further attenuated vaccine candidate strain harboring deletions in two additional genes, htrA and pipA. We determined that S. Typhimurium requires pipA to elicit fluid accumulation in a rabbit ileal loop model of gastroenteritis, as an S. Typhimurium ΔpipA mutant induced significantly less fluid accumulation in rabbit loops than the wild-type strain. New vaccine strain CVD 1926 (I77 ΔguaBA ΔclpP ΔpipA ΔhtrA) was assessed for inflammatory potential in an organoid model of human intestinal mucosa, where it induced less inflammatory cytokine production than organoids exposed to the precursor vaccine, CVD 1921. To assess vaccine safety and efficacy, mice were given three doses of CVD 1926 (10(9) CFU/dose) by oral gavage, and at 1 or 3 months postimmunization, mice were challenged with 700 or 100 LD(50) (50% lethal doses), respectively, of wild-type strain I77. CVD 1926 was well tolerated and exhibited 47% vaccine efficacy following challenge with a high inoculum and 60% efficacy after challenge with a low inoculum of virulent S. Typhimurium. CVD 1926 is less reactogenic yet equally as immunogenic and protective as previous iterations in a mouse model.

We investigated the ability of live attenuatedSalmonella entericaserovar Typhi strains delivered to mice intranasally to induce specific cytotoxic T-lymphocyte (CTL) responses at regional and systemic levels. Mice immunized with two doses (28 days apart) ofSalmonellaserovar Typhi strain Ty21a, the licensed oral typhoid vaccine, and genetically attenuated mutants CVD 908 (ΔaroCΔaroD), CVD 915 (ΔguaBA), and CVD 908-htrA(ΔaroCΔaroDΔhtrA) induced CTL specific forSalmonellaserovar Typhi-infected cells in spleens and cervical lymph nodes. CTL were detected in effector T cells that had been expanded in vitro for 7 days in the presence ofSalmonella-infected syngeneic splenocytes. A second round of stimulation further enhanced the levels of specific cytotoxicity. CTL activity was observed in sorted αβ+CD8+T cells, which were remarkably increased after expansion, but not in CD4+T cells. CTL from both cervical lymph nodes and spleens failed to recognizeSalmonella-infected major histocompatibility complex (MHC)-mismatched cells, indicating that the responses were MHC restricted. Studies in which MHC blocking antibodies were used showed that H-2Ldwas the restriction element. This is the first demonstration thatSalmonellaserovar Typhi vaccines delivered intranasally elicit CD8+MHC class I-restricted CTL. The results further support the usefulness of the murine intranasal model for evaluating the immunogenicity of typhoid vaccine candidates at the preclinical level.

Salmonella enterica serovar Typhi (S. Typhi), the causative agent of typhoid fever, and S. Paratyphi A and B, causative agents of paratyphoid fever, are major public health threats throughout the world. Although two licensed typhoid vaccines are currently available, they are only moderately protective and immunogenic necessitating the development of novel vaccines. A major obstacle in the development of improved typhoid, as well as paratyphoid vaccines is the lack of known immunological correlates of protection in humans. Considerable progress has been made in recent years in understanding the complex adaptive host responses against S. Typhi. Although the induction of S. Typhi-specific antibodies (including their functional properties) and memory B cells, as well as their cross-reactivity with S. Paratyphi A and S. Paratyphi B has been shown, the role of humoral immunity in protection remains undefined. Cell mediated immunity (CMI) is likely to play a dominant role in protection against enteric fever pathogens. Detailed measurements of CMI performed in volunteers immunized with attenuated strains of S. Typhi have shown, among others, the induction of lymphoproliferation, multifunctional type 1 cytokine production, and CD8(+) cytotoxic T-cell responses. In addition to systemic responses, the local microenvironment of the gut is likely to be of paramount importance in protection from these infections. In this review, we will critically assess current knowledge regarding the role of CMI and humoral immunity following natural S. Typhi and S. Paratyphi infections, experimental challenge, and immunization in humans. We will also address recent advances regarding cross-talk between the host's gut microbiota and immunization with attenuated S. Typhi, mechanisms of systemic immune responses, and the homing potential of S. Typhi-specific B- and T-cells to the gut and other tissues.

A common finding when measuring T cell immunity to enteric bacterial vaccines in humans is the presence of background responses among individuals before immunization. Yet the nature of these background responses remains largely unknown. Recent findings show the presence in uninfected individuals of mucosal associated invariant T (MAIT) cells that mount broad spectrum immune responses against a variety of microorganisms including Mycobacterium tuberculosis and enteric bacteria such as Escherichia coli and Salmonella. Therefore, we investigated whether MAIT immune responses to intestinal bacteria might account for the background responses observed before immunization. Here we measured MAIT immune responses to commensal and enteric pathogenic bacteria in healthy individuals with no history of oral immunization with enteric bacteria. We found that MAIT cells were activated by B cells infected with various bacteria strains (commensals and pathogens from the Enterobacteriaceae family), but not by uninfected cells. These responses were restricted by the non-classical MHC-related molecule 1 (MR1) and involved the endocytic pathway. The quality of these responses (i.e., cytokine profile) was dependent on bacterial load but not on the level expression of MR1 or bacterial antigen on B cell surface, suggesting that a threshold level of MR1 expression is required to trigger MAIT activation. These results provide important insights into the role of B cells as a source of antigen-presenting cells to MAIT cells and the gut immune surveillance of commensal microbiota.

Objective : During HIV-1 infection, CD4+ T lymphocytes migrate to immune-reactive lymphoid organs where they are infected by the virus and/or killed by apoptosis on immunoregulatory stimuli - a potential mechanism underlying fatal CD4+ T-cell depletion observed in AIDS. This study seeks to determine the effects of glucocorticoids (GCC) on the activation-induced T-cell apoptosis triggered by HIV-1. Methods : CD4+ and CD8+ T cells were purified from HIV-negative donor peripheral blood mononuclear cells (PBMC) by positive selection and exposed to HIV-1 (primary isolates). HIV-1-exposed CD4+ and CD8+ T cells as well as PBMC derived from HIV-1-infected patients were cultured with medium alone or anti-CD3 monoclonal antibodies (MAb)/mitogens in the presence or absence of hydrocortisone or prednisolone. Viral infection kinetics were assessed by polymerase chain reaction and viral replication was measured by p24 enzyme-linked immunosorbent assay. Cell survival, apoptosis, T-cell proliferation, blast cell transformation, and interleukin (IL)-2 receptor (CD25) expression were monitored in parallel for each cell population. Results : Fractionated CD4+ T cells acutely infected by HIV-1 underwent apoptotic death on anti-CD3 MAb/mitogen stimulation. This activation-induced apoptotic cell killing was antagonized by pharmacological doses of prednisolone or hydrocortisone added up to 6h after stimulation. GCC were also found to be capable of inhibiting the accelerated apoptosis in PBMC (including both CD4+ and CD8+ T-cell fractions) from HIV-1-infected patients. This anti-apoptotic action of GCC overbalanced their downregulatory effect on T-cell proliferation, resulting in an overall improvement of CD4+ T-cell survival in patient PBMC. These effects of GCC were abrogated by the anti-GCC RU 486 and were not associated with significant suppression of CD25 expression and IL-2-dependent T-cell blast transformation ; moreover, GCC had no impact on viral infection and replication. Conclusion : GCC exert a receptor-mediated anti-apoptotic activity in mature T cells through both activation-induced and HIV-1-triggered pathways, and could be potent inhibitors of T-cell apoptosis in HIV-1-infected patients.