Salmonella enterica Serovar Typhimurium Travels to Mesenteric Lymph Nodes Both with Host Cells and Autonomously.

Salmonella infection is a globally important cause of gastroenteritis and systemic disease and is a useful tool to study immune responses in the intestine. Although mechanisms leading to immune responses against Salmonella have been extensively studied, questions remain about how bacteria travel from the intestinal mucosa to the mesenteric lymph nodes (MLN), a key site for Ag presentation. In this study, we used a mouse model of infection with Salmonella enterica serovar Typhimurium (STM) to identify changes in intestinal immune cells induced during early infection. We then used fluorescently labeled STM to identify interactions with immune cells from the site of infection through migration in lymph to the MLN. We show that viable STM can be carried in the lymph by any subset of migrating dendritic cells but not by macrophages. Moreover, approximately half of the STM in lymph are not associated with cells at all and travel autonomously. Within the MLN, STM associates with dendritic cells and B cells but predominantly with MLN-resident macrophages. In conclusion, we describe the routes used by STM to spread systemically in the period immediately postinfection. This deeper understanding of the infection process could open new avenues for controlling it.

Expression of aberrant HLA-B27 molecules is dependent on B27 dosage and peptide supply.

OBJECTIVES: Cellular expression of non-classical forms of human leukocyte antigen (HLA)-B27 (NC-B27) may be involved in spondyloarthritis (SpA) pathogenesis. We used a novel B27-specific monoclonal antibody, HD6, to ask if B27 transgenic (TG) rat splenocytes express these NC-B27 molecules. We also investigated whether B27-binding peptides could affect the expression and functional immune recognition of HD6-reactive B27 molecules. METHODS: Splenocytes from B27-TG, B7-TG and non-transgenic rats, and HLA-B27+ cell lines were stained with monoclonal antibodies recognising classical (ME-1, HLA-ABC-m1) and non-classical (HD6, HC10) B27. Cells were further cultured in the presence of HLA-B27-binding peptides, or subjected to brief low pH treatment prior to mAb staining and/or immunoprecipitation or co-culture with KIR3DL2-CD3ε-expressing Jurkat reporter cells. RESULTS: HD6-reactive molecules were detected in the majority of adult B27-TG rat splenocyte cell subsets, increasing with age and concomitant increased B27 expression. HD6 staining was inhibited by incubation with B27-binding peptides and induced by low pH treatment. HD6 staining correlated with KIR3DL2-CD3ε-expressing Jurkat reporter cell activity. Thus, IL-2 production was decreased when B27-expressing antigen-presenting cells were preincubated with B27-binding peptides, but increased following pretreatment with low pH buffer. CONCLUSIONS: Surface expression of HD6-reactive B27 molecules on B27-TG rat splenocytes is consistent with a pathogenic role for NC-B27 in SpA. Interaction of NC-B27 with innate immune receptors could be critical in SpA pathogenesis, and we show that this may be influenced by the availability and composition of the B27-binding peptide pool.

Dendritic cells and regulatory T cells in spondyloarthritis.

PURPOSE OF REVIEW: The spondyloarthropathies (SpAs) are a group of interrelated inflammatory disorders with overlapping clinical features. Current SpA treatments only provide partial symptomatic and functional relief in a subgroup of patients. Consequently, there is a need to better understand the pathophysiology of SpA to develop more specific and effective treatments for these conditions. RECENT FINDINGS: Genetic and mechanistic evidence links SpA with inflammatory bowel disease (IBD) and psoriasis, and the symptoms of these diseases partially overlap. Regulatory T cells (Tregs) and dendritic cells control the adaptive immune response, and failures in their functions are likely to contribute to the establishment of chronic inflammation. The contributions of Tregs and dendritic cells to IBD and SpA have been assessed in both animal models of disease and patients. SUMMARY: Although defects in Tregs are important in psoriasis and in animal models of IBD, there is little evidence that they are important in SpA. However, data from animal models indicate that dendritic cells drive pathogenic T-cell responses, partly through the production of interleukin-23 (IL-23). Dendritic cells from SpA patients may also contribute to disease by producing IL-23, therefore supporting the differentiation of the Th17 cells that contribute to inflammation. The driving forces in SpA pathophysiology are now becoming clear; these data may lead to the development of novel therapies to target SpA and related inflammatory disorders.

Expression of HLA-B27 causes loss of migratory dendritic cells in a rat model of spondylarthritis.

OBJECTIVE: In rats transgenic for human HLA-B27 and ß(2) -microglobulin (B27-transgenic rats), colitis and peripheral inflammation develop spontaneously. Therefore, B27-transgenic rats provide a model of spondylarthritis. Because inflammation in these rats requires CD4+ T lymphocytes and involves intestinal pathology, we hypothesized that dendritic cells (DCs) that migrate from the intestine and control CD4+ T cell differentiation would be aberrant in B27-transgenic rats. METHODS: Migrating intestinal lymph DCs were collected via thoracic duct cannulation from B27-transgenic and control (HLA-B7-transgenic or nontransgenic) rats. The phenotypes of these DCs and of mesenteric lymph node DCs were assessed by flow cytometry. The ability of DCs to differentiate from bone marrow precursors in vitro was also assessed. RESULTS: Lymph DCs showed increased activation and, strikingly, lacked the specific DC population that is important for maintaining tolerance to self-antigens. This population of DCs was also depleted from the mesenteric lymph nodes of B27-transgenic rats. Furthermore, in vitro culture of DCs from bone marrow precursors revealed a defect in the ability of B27-transgenic rats to produce DCs of the migratory phenotype, although the DCs that were generated induced enhanced interleukin-17 (IL-17) production from naive CD4+ T cells. CONCLUSION: We describe 2 different mechanisms by which HLA-B27 may contribute to inflammatory disease: increased apoptotic death of B27-transgenic DCs that normally function to maintain immunologic tolerance and enhanced IL-17 production from CD4+ T cells stimulated by the surviving B27-transgenic DCs.

Role of Gut Inflammation in Altering the Monocyte Compartment and Its Osteoclastogenic Potential in HLA-B27-Transgenic Rats.

OBJECTIVE: To investigate the relationship between intestinal inflammation and the central and peripheral innate immune system in the pathogenesis of HLA-B27-associated spondyloarthritis using an HLA-B27-transgenic (B27-Tg) rat model. METHODS: The myeloid compartment of the blood and bone marrow (BM) of B27-Tg rats, as well as HLA-B7-Tg and non-Tg rats as controls, was evaluated by flow cytometry. Plasma from rats was assessed by enzyme-linked immunosorbent assay for levels of CCL2 and interleukin-1α (IL-1α). Rats were treated with antibiotics for 4 weeks, and the myeloid compartment of the blood and BM was evaluated by flow cytometry. The osteoclastogenic potential of BM-derived cells from antibiotic-treated rats, in the presence or absence of tumor necrosis factor (TNF), was evaluated in vitro. RESULTS: B27-Tg rats had substantially higher numbers of circulating Lin-CD172a+CD43low monocytes as compared to control animals, and this was significantly correlated with higher levels of plasma CCL2. Antibiotic treatment of B27-Tg rats markedly reduced the severity of ileitis, plasma levels of CCL2 and IL-1α, and number of BM and blood Lin-CD172a+CD43low monocytes, a cell subset shown in the present study to have the greatest in vitro osteoclastogenic potential. Antibiotic treatment also prevented the TNF-dependent enhancement of osteoclastogenesis in B27-Tg rats. CONCLUSION: Microbiota-dependent intestinal inflammation in B27-Tg rats directly drives the systemic inflammatory and bone-erosive potential of the monocyte compartment.