RA patients have elevated levels of total IgA [36,37], and serum levels of IgA and IgG can predict future RA development [38], while serum levels of IgA, but not IgG or IgM, have been associated with the degree of cartilage erosions in patients with established RA for ≥1 year [39]. This evidence concerns the gene CD40LG and rheumatoid arthritis.