IgG4-related kidney disease: from renal histopathology and immunopathogenesis to novel pharmacological interventions

Introduction Immunoglobulin G4 (IgG4)-related disease (IgG4-RD) is a rare and chronic fibroinflammatory condition hallmarked by tumefactive lesions that can affect nearly any organ of the body and lead to fibrotic organ destruction. Parenchymal and non-parenchymal affection of the kidney and urogenital tract are subsumed under the umbrella term IgG4-related kidney disease (IgG4-RKD), which is a severe and quite common organ manifestation in IgG4-RD. The immunopathogenesis in IgG4-RD is depicted by a complex interplay of distinct B and T-cell subsets, excessive antibody production, a unique cytokine environment and the development of exuberant fibrosis. Scientific advancements over the last two decades have fostered to explore a broad repertoire of pharmacological interventions starting from B-cell depleting agents and extending to modulators of T-cell co-stimulation.