272. Dissecting Host-Commensal Interactions During Early Life to Identify Mechanisms of Protection Against Autoimmune Diabetes

Abstract

Abstract Background Major Histocompatibility Complex (MHC) and Human Leukocyte Antigen (HLA) loci have strong genetic linkage with type 1 diabetes (T1D) in mice and humans, respectively. The diabetes-prone non-obese diabetic (NOD) strain of mice have a unique MHC-II locus with a distinct MHC-II A molecule (Ag7) and lack expression of the MHC-II E molecule. Expression of this MHC-II A molecule is associated with development of T1D, whereas transgenic restoration of the MHC-II E molecule dominantly protects against T1D. The Silverman laboratory recently demonstrated that MHC-II E molecule expression selects for a diabetes-protective intestinal microbiota in early life though a key knowledge gap remains: how do these two factors — MHC-II molecules and commensal microbiota — work together during a critical early-life period of microbiome and immune system ontogeny to prevent T1D? To address this question, the Silverman laboratory developed a gnotobiotic mouse model by designing a microbial community consisting of 9 intestinal microbes cultured from these diabetes-protected (Ea16/NOD) mice – called “PedsCom”. This gnotobiotic model allows for mechanistic, well-controlled studies of interactions between commensal microbes and the developing immune system. Methods We used flow cytometry to sort commensal bacteria from PedsCom-colonized NOD and Ea16/NOD mice into IgA-coated and IgA-uncoated populations. We employed species-specific multiplex qPCR to quantify relative abundance of each PedsCom microbe in these sorted populations. Results Two microbes, K. cowanii and L. murinus, were preferentially IgA bound in both NOD and Ea16/NOD mice. L. johnsonii, A. caccae, and S. xylosus were preferentially IgA bound only in the presence of MHC-II E molecule expression. Many of the highly IgA coated microbes (K. cowanii, L. murinus, L, johnsonii, and A. caccae) translocate to the mesenteric lymph nodes. Conclusion: We propose that MHC-II expression facilitates specific mucosal IgA responses, that MHC-II E expression allows for additional epitope recognition amongst PedsCom members which may potentiate this effect, and that preferential IgA coating may promote contact with mucosa-associated lymphoid tissues as early steps in tolerogenic immune system ontogeny that protects against development of T1D. Disclosures All Authors: No reported disclosures