KM55 Monoclonal Antibody Staining in IgA-Dominant Infection-Related Glomerulonephritis

IgA-dominant infection-related glomerulonephritis (IgA-IRGN) is a unique form of IRGN, which needs to be distinguished from IgA nephropathy (IgAN), due to overlapping clinical and pathological features. The key factor in the pathogenesis of IgAN is galactose-deficient IgA1 (Gd-IgA1). However, the mechanism of glomerular IgA deposition in patients with IgA-IRGN is unclear. Therefore, we evaluated whether Gd-IgA1 could be a useful biomarker to distinguish between these 2 diseases.A case-control study was conducted to analyze the clinical and pathological characteristics of 12 patients with IgA-IRGN. The intensity and distribution of glomerular Gd-IgA1 (KM55) staining in renal biopsies were assessed. The control group consisted of 15 patients diagnosed with IgAN and an additional 17 patients with glomerulopathy involving IgA deposition.The main clinical manifestations of patients with IgA-IRGN were nephrotic-range proteinuria, hematuria, acute renal injury, and hypocomplementemia. Active lesions were the leading pathological feature, while focal segmental sclerosis was rare. Half of the patients exhibited hump-shaped subepithelial deposits. Glomerular KM55 staining was negative in 7 patients, trace in 4 patients, and 2+ in 1 patient. The median intensity of KM55 staining in IgA-IRGN patients was 0 (range 0∼2+), which was significantly lower than that of primary IgAN patients (median 2+, range 1+∼3+). The receiver operating characteristic analysis demonstrated that the optimal cutoff level to identify these 2 diseases was 0.5+.Glomerular KM55 staining intensity might be helpful to distinguish IgA-IRGN from primary IgAN. Weak or negative staining may favor IgA-IRGN. In addition, integrated analysis including clinical data, pathological findings, and prognostic information would further improve the differential diagnosis.