There is increasing evidence that commensal and pathogenic gut microbiota alter susceptibility to multiple sclerosis (MS), rheumatoid arthritis, type I diabetes, and systemic lupus erythematosus.39, 40 In this report, we observed a striking sequence homology between the AQP4 T-cell epitope p63–76, which contains predicted binding motifs for 2 NMO-associated HLA-DR molecules,41 and p204–217 of a C. perfringens ABC-TP. The gene discussed is AQP4; the disease is rheumatoid arthritis.