Background/Purpose: Autoantibodies reactive against Ro60 protein are often found in patients with Sjogren’s syndrome.  This study was undertaken to investigate the role of oral and gut microbiota in initiation of autoimmune responses against Ro60.  We hypothesized that proteins derived from oral/gut microbes activate Ro60 reactive T cells, which then play a critical role in autoantibody generation.

Methods: HLA-DR3 restricted T cell hybridomas, reactive against Ro60 were generated, and employed to map and characterize T cell epitopes on Ro60.  Pattern search and BLAST analysis was carried out to identify putative cross-reactive peptides from microbes in the Human Oral Microbiome Database.  Several peptides were synthesized and their ability to activate Ro60 reactive T cell hybridomas tested.  A recombinant microbial protein that contained the strongest mimicry peptide was generated and its ability to activate Ro60 reactive T cells analyzed.  HLA-DR3 transgenic mice were immunized with this microbial protein and autoantibody responses against different autoantigens investigated.

Results: The HLA-DR3 restricted T cell hybridomas recognized 3 epitopes on Ro60, Ro60_221-250, Ro60_241-260 and Ro60_361-390.  Pattern search analysis identified several hundred mimicry peptides originating from oral and gut microbes.  Amongst these, peptides originating from von Willebrand factor type A (vWFA) protein were most potent in activating T cell hybridoma reactive against Ro60_361-390.  Purified recombinant vWFA protein from Capnocytophaga ochracea (an oral microbe) activated Ro60 reactive T cells.  Interestingly, whole E coli expressing vWFA protein were also able to activate Ro60 reactive T cells.  These results show that peptides from vWFA protein are processed and presented by antigen presenting cells even in the presence of hundreds of other E coli proteins.  Immunization of HLA-DR3 transgenic mice with recombinant vWFA protein readily induced autoantibodies reactive against Ro60, La (SSB) and Ro52 (SSA).

Conclusion: Our results clearly demonstrate that a microbial protein present in different commensall oral/gut bacteria can activate Ro60 reactive T cells and induce autoantibody responses against Ro60.  Thus, we would like to propose that a dysregulated immune response against normal microbiome can be one of the pathways responsible for initiating autoimmune responses in Sjogren’s syndrome.  Considering that oral infections are a common problem in Sjogrens’s syndrome patients, this pathway might also be involved in amplification of autoimmune responses in this disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/oral-and-gut-microbiota-influence-immune-responses-to-sjogrens-syndrome-associated-antigen-ro60/