Abstract
Objective: To determine whether the absence of mesangial IgG deposits is associated with the absence of elevated blood levels of galactose-deficient IgA1 (Gd-IgA1) in pediatric patients with IgA nephropathy (IgAN). Design and methods: Serum Gd-IgA1 levels were determined by ELISA using an N-acetylgalactosamine-specific lectin from Helix aspersa. Levels of Gd-IgA1 above the 90th percentile for healthy pediatric controls were considered to be elevated. Renal biopsy samples were examined by immunofluorescence for presence and intensity of staining for IgA, IgG, IgM, C3 and C1q and by light microscopy for histological changes. Findings were graded by a single pathologist (L. Gaber) at UTHSC until 2007 and by NephropathTM (Little Rock, AR, USA) thereafter. Staining for the mesangial deposits was considered negative when intensity was trace or less, and positive at greater intensity. Fisher’s exact-test was used to determine significance of 2 × 2 tables. Results: Serum samples were obtained from 30 patients with IgAN diagnosed before age 18 years. Male : female ratio was 2.3 : 1. Twenty were Caucasian and 10 were African-American. Blood was obtained within 3 months of biopsy (incident cases) for 12, while 18 provided blood > 3 months after biopsy (prevalent cases). Serum Gd-IgA1 level was elevated in 23 (77%) of cases and 20 (67%) had a biopsy positive for IgG. Of those 20 patients, 18 (90%) had an elevated serum Gd-IgA1 level, whereas 5 (50%) of patients with biopsies without IgG had a normal serum Gd-IgA1 level (p = 0.026). Summary: In this small study we found a weak association between the absence of IgG in the biopsy and normal serum Gd-IgA1 level.
Highlights
To determine whether the absence of mesangial IgG deposits is associated with the absence of elevated blood levels of galactose-deficient IgA1 (Gd-IgA1) in pediatric patients with IgA nephropathy (IgAN)
IgA nephropathy (IgAN) is an autoimmune renal disease resulting from aberrant glycosylation of IgA1 in the hinge-region O-linked glycans
galactose and thus terminate with N-acetylgalactosamine (GalNAc) can be recognized by anti-glycan IgG antibodies, resulting in formation of immune complexes either in situ in the mesangium or in the circulation that can subsequently deposit in the mesangium [1, 2, 3]
Summary
IgA nephropathy (IgAN) is an autoimmune renal disease resulting from aberrant glycosylation of IgA1 in the hinge-region O-linked glycans. We have previously shown that 75% of pediatric patients with IgAN have elevated serum levels of galactose-deficient IgA1 (GdIgA1) [4]. It is not known whether Gd-IgA1 is recognized by cross-reactive antibodies originally induced by a mucosal pathogen, for example, or whether Gd-IgA1 may be inducing these IgG autoantibodies. As many adult patients with IgAN do not have IgG co-deposits [5], we assessed whether pediatric patients with IgAN exhibit an association between presence of IgA deposits and serum Gd-IgA1 level. In theory, such an association would be supportive of the immunogenic character of Gd-IgA1 in IgAN
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