IgG4-related disease: pathophysiologic insights drive emerging treatment approaches.

IgG4-related disease (IgG4-RD) is a fibroinflammatory condition that can affect essentially any organ. The disease shows similar histopathology findings across organ systems, consisting of a lymphoplasmacytic infiltrate enriched in IgG4-positive plasma cells, storiform fibrosis, and obliterative phlebitis. IgG4 itself appears to be a reactive phenomenon rather than the primary disease driver. Recent investigations have focused on the interactions between cells of the B cell lineage and a novel CD4+ SLAMF7+ cytotoxic T cells capable of promoting fibrosis. Plasmablasts appear to play a crucial role along with B cells in the presentation of antigen to this T cell. IgG4-RD is marked by responsiveness to glucocorticoids, but frequent disease relapse, the inability to taper glucocorticoids completely, and steroid toxicity are problematic. Targeted treatment approaches against the B cell lineage appear promising, and therapeutic efforts focused upon the CD4+ SLAMF7+ cytotoxic T cell may also be feasible.