KM55 Monoclonal Antibody and IgA Variant of Proliferative Glomerulonephritis With Monoclonal Ig Deposits

摘要

Proliferative glomerulonephritis with monoclonal IgG deposits (PGNMID) is characterized by mono- typic IgG deposition, most commonly IgG3- k . Mono- clonal Ig, albeit less commonly, may also consist of IgM, or rarely IgA, with k - or l -light chain restriction. Recently, a multicenter study including 14 patients and a few case reports described the possibility of a monoclonal IgA variant of PGNMID. 1–9,S1 IgA ne- phropathy (IgAN) is frequently seen worldwide, and galactose-deficient IgA1 (Gd-IgA1) has been identified as the key pathogenic factor in IgAN. Owing to the increased affinity of polymeric IgA l binding to mesan- gial cells, S2 a certain ratio of light chain–restricted pri- mary IgAN (especially l -restricted) was observed, which makes it difficult to differentiate between light chain–restricted primary IgAN and IgA variant of PGNMID using routine immunofluorescence (IF). To the best of our knowledge, this is the first report of 2 cases of IgA variant of PGNMID (IgA- l ) that exhibited membranoproliferative glomerulonephritis with nega- tive Gd-IgA1-specific monoclonal antibody (KM55) staining. However, KM55 monoclonal antibody was positive in other l -restricted primary IgAN, suggesting that the staining of KM55 monoclonal antibody could be a powerful tool to differentiate between monoclonal IgA variant of PGNMID and light chain–restricted pri- mary IgAN.