CD79A and rheumatoid arthritis: The mucosal origin hypothesis (56) suggested that the mucosa is the earliest site of RA-associated autoantibodies and that elevated levels of various types of RA-associated IgA in RA patients precede the onset of clinical arthritic symptoms (57, 58), while the homologous immune cells were found in the gut and joints of RA patients (59, 60), suggesting that gut-derived immunity in the preclinical phase is relevant to the pathogenesis of RA.