The systemic anti-microbiota IgG repertoire can identify gut bacteria that translocate across gut barrier surfaces

Unique gut microbiota compositions have been associated with inflammatory diseases, but identifying gut bacterial functions linked to immune activation in humans remains challenging. Translocation of pathogens from mucosal surfaces into peripheral tissues can elicit immune activation, although whether and which gut commensal bacteria translocate in inflammatory diseases is difficult to assess. We report that a subset of commensal gut microbiota constituents that translocate across the gut barrier in mice and humans are associated with heightened systemic immunoglobulin G (IgG) responses. We present a modified high-throughput, culture-independent approach to quantify systemic IgG against gut commensal bacteria in human serum samples without the need for paired stool samples. Using this approach, we highlight several commensal bacterial species that elicit elevated IgG responses in patients with inflammatory bowel disease (IBD) including taxa within the clades