High Chlamydia Burden Promotes Tumor Necrosis Factor-Dependent Reactive Arthritis in SKG Mice

OBJECTIVE

Chlamydia trachomatis is a sexually transmitted obligate intracellular pathogen that causes inflammatory reactive arthritis, spondylitis, psoriasiform dermatitis, and conjunctivitis in some individuals after genital infection. The immunologic basis for this inflammatory response in susceptible hosts is poorly understood. As ZAP-70(W163C) -mutant BALB/c (SKG) mice are susceptible to spondylo-arthritis after systemic exposure to microbial β-glucan, we undertook the present study to compare responses to infection with Chlamydia muridarum in SKG mice and BALB/c mice.

METHODS

After genital or respiratory infection with C muridarum, conjunctivitis and arthritis were assessed clinically, and eye, skin, and joint specimens were analyzed histologically. Chlamydial major outer membrane protein antigen-specific responses were assessed in splenocytes. Treg cells were depleted from FoxP3-DTR BALB/c or SKG mice, and chlamydial DNA was quantified by polymerase chain reaction.

RESULTS

Five weeks after vaginal infection with live C muridarum, arthritis, spondylitis, and psoriasiform dermatitis developed in female SKG mice, but not in BALB/c mice. Inflammatory bowel disease did not occur in mice of either strain. The severity of inflammatory disease was correlated with C muridarum inoculum size and vaginal burden postinoculation. Treatment with combination antibiotics starting 1 day postinoculation prevented disease. Chlamydial antigen was present in macrophages and spread from the infection site to lymphoid organs and peripheral tissue. In response to chlamydial antigen, production of interferon-γ and interleukin-17 was impaired in T cells from SKG mice but tumor necrosis factor (TNF) responses were exaggerated, compared to findings in T cells from BALB/c mice. Unlike previous observations in arthritis triggered by β-glucan, no autoantibodies developed. Accelerated disease triggered by depletion of Treg cells was TNF dependent.

CONCLUSION

In the susceptible SKG strain, Chlamydia-induced reactive arthritis develops as a result of deficient intracellular pathogen control, with antigen-specific TNF production upon dissemination of antigen, and TNF-dependent inflammatory disease.

Role of genetics in infection-associated arthritis

Genetic discoveries in arthritis and their associated biological pathways spanning the innate and adaptive immune system demonstrate the strong association between susceptibility to arthritis and control of exogenous organisms. The canonical theory of the aetiology of immune-mediated arthritis and other immune-mediated diseases is that the introduction of exogenous antigenic stimuli to a genetically susceptible host sets up the environment for an abnormal immune response manifesting as disease. A disruption in host-microbe homeostasis driven by disease-associated genetic variants could ultimately provide the source of exogenous antigen triggering disease development. We discuss genetic variants impacting the innate and adaptive arms of the immune system and their relationship to microbial control and arthritic disease. We go on to consider the evidence for a relationship between HLA-B27, infection and arthritis, and then emerging evidence for an interaction between microbiota and rheumatoid arthritis.

Interleukin-23 mediates the intestinal response to microbial β-1,3-glucan and the development of spondyloarthritis pathology in SKG mice

OBJECTIVE

Spondyloarthritides (SpA) occur in 1% of the population and include ankylosing spondylitis (AS) and arthropathy of inflammatory bowel disease (IBD), with characteristic spondylitis, arthritis, enthesitis, and IBD. Genetic studies implicate interleukin-23 (IL-23) receptor signaling in the development of SpA and IBD, and IL-23 overexpression in mice is sufficient for enthesitis, driven by entheseal-resident T cells. However, in genetically prone individuals, it is not clear where IL-23 is produced and how it drives the SpA syndrome, including IBD or subclinical gut inflammation of AS. Moreover, it is unclear why specific tissue involvement varies between patients with SpA. We undertook this study to determine the location of IL-23 production and its role in SpA pathogenesis in BALB/c ZAP-70(W163C)-mutant (SKG) mice injected intraperitoneally with β-1,3-glucan (curdlan).

METHODS

Eight weeks after curdlan injection in wild-type or IL-17A(-/-) SKG or BALB/c mice, pathology was scored in tissue sections. Mice were treated with anti-IL-23 or anti-IL-22. Cytokine production and endoplasmic reticulum (ER) stress were determined in affected organs.

RESULTS

In curdlan-treated SKG mice, arthritis, enthesitis, and ileitis were IL-23 dependent. Enthesitis was specifically dependent on IL-17A and IL-22. IL-23 was induced in the ileum, where it amplified ER stress, goblet cell dysfunction, and proinflammatory cytokine production. IL-17A was pathogenic, while IL-22 was protective against ileitis. IL-22+CD3- innate-like cells were increased in lamina propria mononuclear cells of ileitis-resistant BALB/c mice, which developed ileitis after curdlan injection and anti-IL-22.

CONCLUSION

In response to systemic β-1,3-glucan, intestinal IL-23 provokes local mucosal dysregulation and cytokines driving the SpA syndrome, including IL-17/IL-22-dependent enthesitis. Innate IL-22 production promotes ileal tolerance.