Serum anti-streptococcal IgA, IgG and IgM antibodies in IgA-associated diseases.

Serum anti-streptolysin-O antibody (ASO) and anti-streptococcal polysaccharide antibody (ASP) of IgA, IgG and IgM classes were measured using an enzyme-linked immunosorbent assay in 41 children with IgA nephropathy (Group A), 15 children with uncomplicated anaphylactoid purpura (Group B) and 13 children with purpura nephritis (Group C). The serum concentrations of the IgA, IgG and IgM classes were measured by single radial immunodiffusion. When compared with sex- and age-matched controls, the concentrations of serum IgA (but not of IgG or IgM) were significantly increased in the three groups studied. The titers of ASO of the IgA and IgM classes, and those of ASP of the IgA and IgG classes, were significantly increased in Group A. In Group B, only the ASP titers of the IgA class were significantly increased. No significant difference was noted in the titers of either ASO or ASP of any class in Group C. Thus, increased antibody response in IgA nephropathy is not restricted to IgA. Anaphylactoid purpura with or without renal disease appears to be different in its humoral anti-streptococcal response from IgA nephropathy.