Outer Membrane Protein of Gut Commensal Microorganism Induces Autoantibody Production and Extra-Intestinal Gland Inflammation in Mice

Gut commensal microorganisms have been linked with chronic inflammation at the extra-intestinal niche of the body. The object of the study was to investigate on the chronic effects of a gut commensal Escherichia coli on extra-intestinal glands. The presence of autoimmune response was diagnosed by autoantibody levels and histological methods. Repeated injection of E. coli induced mononuclear cell inflammation in the Harderian and submandibular salivary glands of female C57BL/6 mice. Inflammation was reproduced by adoptive transfer of splenocytes to immune-deficient Rag2 knockout mice and CD4(+) T cells to mature T cell-deficient TCRβ-TCRδ knockout mice. MALDI TOF mass spectrometry of the protein to which sera of E. coli-treated mice reacted was determined as the outer membrane protein A (OmpA) of E. coli. Multiple genera of the Enterobacteriaceae possessed OmpA with high amino-acid sequence similarities. Repeated injection of recombinant OmpA reproduced mononuclear cell inflammation of the Harderian and salivary glands in mice and elevation of autoantibodies against Sjögren’s-syndrome-related antigens SSA/Ro and SSB/La. The results indicated the possibility of chronic stimuli from commensal bacteria-originated components as a pathogenic factor to elicit extra-intestinal autoimmunity.