CD79A and immunoglobulin G4-related sclerosing disease: Though there are few studies on the role of IgA in IgG4-RD, a recent study has reported that patients with relapse had significantly higher levels of serum IgG4 but lower levels of serum IgA compared to patients without relapse [30], and the lower level of serum IgA is used to differentiate IgG4-RD from hyper-interleukin (IL-) 6 syndromes such as multicentric Castleman’s disease [36, 37].