Contribution of macromolecular IgA1 to IgA abnormality in IgA nephropathy

To evaluate the contribution of macromolecular IgA1 to IgA abnormality in childhood IgA nephropathy, serum samples from 29 healthy children and 26 patients with IgA nephropathy in different age-groups (7-9, 10-12, and 13-15 years) were each separated by sucrose density gradient ultracentrifugation and assayed for IgA1 using an enzyme-linked immunosorbent assay. IgA1 in fraction I (sedimentation coefficient >11.4s) was significantly greater in patients 7-15 years of age (median 36.3-57.0 mg/dl) than in the age-matched controls (median 8.8-10.4 mg/dl). IgA1 in fraction II (11.4-9.3s) was significantly greater in patients 10-15 years of age (median 46.7-52.6 mg/dl) than in the controls (median 27.8-35.5 mg/dl), and IgA1 in fraction III (<9.3s) was significantly greater in patients 13-15 years of age (median 156.9 mg/dl) than in the controls (median 120.7 mg/dl). The ratio of IgA1 in fractions I-III was higher in the patients of each age-group (median 0.233-0.314) than in the controls (median 0.067-0.082), while the ratio of IgA1 in fractions II-III was not significantly high in patients 7-12 years old (median 0.268 to 0.318) compared with the controls (median 0.182-0.264). Thus, IgA abnormality in childhood IgA nephropathy would be better represented by an increase in macromolecular IgA1 of >11.4s than by an increase in IgA1 in fractions of 11.4-9.3s or <9.3s.