Reduced responsiveness of HLA-B27 transgenic rat cells to TGF-beta and IL-10-mediated regulation of IFN-gamma production

Antigen-presenting cell production of IL-10 inhibits T-helper 1 and 17 cell responses and suppresses colitis in mice

BACKGROUND & AIMS

Mice that are deficient in interleukin (IL)-10 develop colitis, mediated by T-helper (Th)1 and Th17 cells, and IL-10-producing regulatory T (Treg) cells suppress colitis, implicating IL-10 in maintaining mucosal homeostasis. We assessed the relative importance of immunoregulatory IL-10 derived from T cells or from antigen presenting cells (APCs) in development of intestinal inflammation.

METHODS

CD4(+) cells from germ-free (GF) or specific pathogen-free (SPF) IL-10(-/-) or wild-type mice were injected into IL-10(-/-), Rag2(-/-) mice or Rag2(-/-) mice that express IL-10. After 6-8 weeks, we evaluated inflammation, spontaneous secretion of cytokines from colonic tissue, and mRNA levels of the transcription factor T-bet and the immunoregulatory cytokine transforming growth factor (TGF)-β. CD4(+) T cells were co-cultured with bacterial lysate-pulsed APCs and assayed for cytokine production, FoxP3 expression, and TGF-β-mediated Smad signaling.

RESULTS

CD4(+) cells from GF or SPF IL-10(-/-) or wild-type mice induced more severe colitis and higher levels of inflammatory cytokines in IL-10(-/-), Rag2(-/-) mice than in IL-10-replete, Rag2(-/-) mice. Co-cultures of IL-10(-/-) or wild-type CD4(+) T cells plus bacterial lysate-pulsed APCs from IL-10(-/-) mice contained more interferon (IFN)-γ, IL-12/23p40, and IL-17 than co-cultures of the same T cells plus APCs from wild-type mice. CD11b(+) APCs were required for these effects. Blocking IL-10 receptors increased production of IFN-γ and IL-12/23p40 whereas exogenous IL-10 suppressed these cytokines. IL-10-producing APCs induced TGF-β-mediated, retinoic acid-dependent, differentiation of FoxP3(+) Treg cells, whereas blocking the retinoic acid receptor, in vitro and in vivo, reduced proportions of FoxP3(+) Treg cells.

CONCLUSIONS

IL-10 produced by APCs regulates homeostatic T-cell responses to commensal bacteria.

The Role of HLA-B27 in Spondyloarthritis

This article summarizes the proceedings of a one-day international workshop held in July 2009 on the role of HLA-B27 in the pathogenesis of ankylosing spondylitis (AS) and related disorders. HLA-B27 is found in about 90% of patients with AS, with an odds ratio of about 100, but the mechanism underlying this association is not known. There are currently 3 major mechanistic hypotheses for this association: (1) T cell recognition of one or more B27 presented peptides; (2) B27 heavy-chain misfolding that induces an unfolded protein response; and (3) innate immune recognition of cell-surface expressed B27 heavy-chain dimers. None of these hypotheses accounts for the tissue specificity of the inflammation characteristic of AS. These hypotheses were discussed in the context of known epidemiologic, biochemical, structural, and immunologic differences among HLA-B27 subtypes; data from the HLA-B27 transgenic rat model of spondyloarthritis; the growing list of other genes that have been found to be associated with AS; and other data on the pathogenesis of spondyloarthritis. Proposed directions for future research include expanded efforts to define similarities and differences among the B27 subtypes; further development of animal models; identifying the interactions of B27 with the products of other genes associated with AS; and continued investigation into the pathogenesis of spondyloarthritis.