IgA and IgG-Seq in Crohn's disease with or without spondyloarthritis

Joint inflammation is the most common extra-intestinal manifestation of Crohns disease (CD). Although alterations in the enteric microbiota are associated with CD with spondyloarthitis (CD-SpA), it is not known whether distinct taxa serve as markers for clinical subtypes of axial (AxSpA) or peripheral SpA (SpA) in CD. Moreover, it is not yet known if these taxa generate specific systemic IgG.We sequenced the fecal microbiome from 106 individuals (44 CD, 39 CD-SpA, 14 CD-AxSpA, and 9 healthy controls (HC)). Using autologous serum, we identified enteric bacteria recognized by serum IgG, and demonstrate differences in IgG coating index of specific bacterial genera associated with CD-SpA. The IgG coating index of Mediterraneibacter gnavus differentiated patients with CD-SpA, and is positively associated with joint disease activity. This work demonstrates divergent microbiome compositions in CD-SpA subgroups, as well as divergent recognition by serum IgG. These results have the potential to serve as a marker of joint inflammation in CD.