Background/Purpose: The earliest autoantibodies in lupus are directed against the autoantigen Ro60, an RNA binding protein with orthologs that we identified in a subset of skin, oral, and gut commensal species. Thus we hypothesized that commensal Ro60 orthologs may trigger autoimmunity via epitope cross-reactivity in genetically susceptible individuals.

Methods: V4 16S rDNA samples from SLE and control subjects were sequenced using 2x250bp paired-end reads on the Illumina MiSeq platform and also tested for species-specific enrichment for Ro60 bacteria by real-time PCR. Co-immuniprecipitation was performed using human SLE serum and Ro60 ortholog-containing Propionibacterium propionicum and Bacteroides thetaiotaomicron lysates. A northern blot of the resulting RNA was probed for bacterial Y RNA. Memory CD4 T cells from SLE patients were sorted into CCR6+ and CCR6- populations. Ro60-specific T cell clones were isolated and stimulated with heat-killed bacteria. Germ-free mice in gnotobiotic isolators were monocolonized by oral gavage with B. thetaiotaomicron. Serum was tested for anti-Ro60 antibodies by ELISA. Lymphocytes from mesenteric lymph node and spleen were stimulated with recombinant Ro60 and proliferation was assessed using a luminescent cell viability assay.

Results: Ro60-producing oral and gut commensals were prevalent in healthy controls and lupus patients. However, when human serum was used to co-immmunoprecipitate Ro60 and its bound Y RNA from a skin commensal, P. propionicum, only antibodies from human Ro60-positive lupus patients bound commensal Ro60. Lack of reactivity in Ro60-negative patients or healthy controls suggested antibody cross-reactivity between human and commensal Ro60. Next, Ro60 autoantigen-specific CCR6+ and CCR6- CD4 memory T cells clones from lupus patients were isolated and expanded using a T cell library assay. Ro60 T cell clones positive for the tissue-homing marker CCR6 proliferated in response to P. propionicum, demonstrating T cell cross-reactivity with commensal Ro60. Finally, germ-free mice were monocolonized with B. thetaiotaomicron. Mesenteric lymph node and spleen cells from monocolonized mice proliferated in response to bacterial Ro60 and sera contained anti-human Ro60 IgG antibodies.

Conclusion: Ro60 autoimmune T and B cells from human lupus patients reacted with commensal Ro60 in vitro, and commensal Ro60 triggered anti-human Ro60 responses in vivo. Taken together, these data support that colonization with autoantigen ortholog-producing species may induce and sustain chronic autoimmunity in lupus. This concept may apply more broadly to human autoimmune diseases and could lead to development of novel microbiota-targeted approaches to treat autoimmunity.

« Back to 2016 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/commensal-ro60-autoantigen-ortholog-cross-reactivity-in-human-lupus-and-gnotobiotic-models/