Cytokines produced by innate immune cells in IgG4-related disease.

IgG4-related disease (IgG4-RD) is a newly defined multi-organ disease proposed by Japanese physicians. IgG4-RD is characterized by elevated serum levels of IgG4 and massive infiltration of IgG4-expressing plasma cells in the affected organs. Recent studies have shown that abnormal adaptive immune responses mediated by T helper type 2 cells, regulatory T cells, follicular helper T cells, cytotoxic CD4+ T cells, and plasmablasts are involved in IgG4-RD immunopathogenesis. In addition to adaptive immune responses, innate immune responses play pathogenic roles in IgG4-RD. Plasmacytoid dendritic cells (pDCs), M2 macrophages, and basophils are activated to produce various kinds of cytokines in IgG4-RD. Recent studies highlight the importance of type I IFN and IL-33 produced by pDCs in IgG4-RD immunopathogenesis.