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Abstract
IgA1 proteins from sera of patients with IgA nephropathy (IgAN) are galactosylated
to a lesser degree than those from healthy controls. The increased reactivity of intact
or de-sialylated serum IgA1 with N-acetylgalactosamine (GalNAc)-specific lectins,
Helix aspersa (HAA) and Caragana arborescens (CAA) and de-sialylated IgA1 with Helix
pomatia (HPA) and Bauhinia purpurea (BPA) indicated that the Gal deficiency is in
glycans located in the hinge region of IgA1 molecules. De-sialylated IgA from sera
of 81 IgAN patients bound biotin-labeled lectin HAA more effectively than did de-sialylated
IgA from 56 healthy controls (P < 0.0001). Similar results were observed for 67 IgAN
patients and 52 controls with second lectin, CAA (P < 0.001). The binding patterns
for 9 patients with mesangial proliferative glomerulonephritis of non-IgA origin were
similar to those for controls. Incompletely galactosylated IgA1 capable of binding
GalNAc-specific lectins was detected in complexes with IgG as demonstrated by ELISA,
size-exclusion chromatography and sucrose gradient ultracentrifugation. The formation
of IgA1-IgG complexes may affect the serum level of IgA1 by reducing the rate of its
elimination and catabolic degradation by the liver.