IgG4-related disease and the kidney.

IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory condition that involves almost every organ system. In this Review, we summarize current knowledge of IgG4-RD and its most frequent manifestations in the kidney—IgG4-related tubulointerstitial nephritis (TIN) and membranous glomerulonephropathy (MGN). Diagnosis of IgG4-RD relies on histopathology: the typical features are a dense lymphoplasmacytic infiltrate and storiform fibrosis. A high percentage of plasma cells observed within lesions stain positively for IgG4. IgG4-related TIN bears the hallmark pathological findings of IgG4-RD; distinctive radiographic characteristics are also frequently observed with use of contrast-enhanced CT. MGN secondary to IgG4-RD seems to be distinct from idiopathic MGN. Humoral and cell-mediated immunity seem to have roles in the pathophysiology of IgG4-RD, but the details of these roles remain unclear. The IgG4 molecule itself is unlikely to be the primary driver of inflammation; rather, it probably downregulates the immune response. Fibrosis might be caused by activation of innate immune cells by polarized CD4(+) T cells. Glucocorticoids are the standard initial treatment for IgG4-RD, but their long-term adverse effects and the high frequency of relapse and renal damage associated with use of this treatment has prompted a search for more effective options. B-cell depletion and the targeting of plasmablasts are both promising approaches.