Charge distribution of plasma IgA in IgA nephropathy.

The spectrotype of plasma IgA in patients with IgA nephropathy was studied by isoelectric focussing. Densitometry of the gels showed a significant increase in the anionic region at isoelectric points (pI) 4.7-5.1 (P = 0.02) and a reduction in the cationic region pI 5.8-6.0 (P = 0.03) in patients (n = 15) compared with controls (n = 8). Measurement of the IgA concentration in eluates of sequential slices of the gels showed that the ratio of anionic-to-cationic IgA, using pI 5.6 as the dividing point, was significantly greater in patients (n = 10) than in controls (n = 10) (P = 0.03). Two different methods of analysis have therefore demonstrated an increased proportion of anionic and decreased proportion of cationic IgA in the plasma of patients with IgA nephropathy.