Heavy and Light Chain Composition of Serum IgA and IgA Rheumatoid Factor in Henoch-Schönlein Purpura

Objective: To characterize the heavy and light chain composition of serum IgA and IgA rheumatoid factor (RF) in 34 children with Henoch-Schönlein purpura (HSP).

Methods: Serum IgA and IgA subclass concentrations were measured by radial immunodiffusion. IgA-RF and the light chain composition of serum IgA and IgA-RF were determined by enzyme immunoassay.

Results: Serum IgA and IgA1 concentrations were higher in HSP patients than controls (P = 0.0001), but there was no difference in IgA2 concentrations between the two groups. IgA-RF was present in 19 of 34 HSP patients; it was composed predominantly of IgA1. The kappa:lambda ratio of serum IgA was virtually identical in patients and controls, but the kappa:lambda ratio of IgA-RF was significantly higher than that of the serum IgA from the 19 IgA-RF seropositive patients (P = 0.0003).

Conclusion: Serum IgA1 is preferentially increased in children with HSP, but the light chain composition of IgA is not different from that in controls. IgA-RF is common in HSP; it is composed predominantly of IgA1 and it is enriched in kappa light chains.