Aberrant signaling in tonsillar B cells producing pathogenic -glycoforms of IgA1 in IgA nephropathy.

IgA nephropathy (IgAN) is a mesangioproliferative glomerulonephritis characterized by IgA1-containing immune-complex deposits wherein IgA1 is enriched for galactose-deficient IgA1 (Gd-IgA1) glycoforms. IgAN pathogenesis involves mucosal immune system, as IgAN onset and activity are associated with infections of the upper-respiratory tract, i.e., synpharyngitic hematuria. Current four-hit hypothesis postulates that multiple events, starting with the production of Gd-IgA1, in genetically susceptible individuals lead to the formation of nephritogenic immune complexes and development of IgAN. Biochemical studies using IgA1-producing cell lines derived from the peripheral blood of IgAN patients and healthy controls revealed that secretion of Gd-IgA1 is due to dysregulated expression of several -glycosylation enzymes. Production of Gd-IgA1 can be further upregulated by some cytokines. Genome-wide association studies identified multiple candidate genes for IgAN, serum levels of IgA, and serum levels of Gd-IgA1. Some of the IgAN-associated genes are also found in other autoimmune diseases and conditions. Notably, locus is associated with IgAN, serum levels of IgA, and tonsillectomy. In this review, we detail various findings concerning IgAN and Gd-IgA1 production by cells derived from the circulation and tonsils. Also, as tonsillectomy is commonly used in Japan as a part of treatment for IgAN, we detail biochemical and signaling studies of IgA1-producing cells derived from peripheral blood and tonsils.