Henoch-Schönlein purpura.

Henoch-Schönlein purpura probably results from a reaction in a host sensitized by an infective stimulus. This stimulus leads to the synthesis of IgA antibody, the presence of circulating immune complexes and a leukoclastic vasculitis involving IgA resulting in renal and dermatological manifestations. The risk factors, the causal organism and the reason for the association with IgA nephropathy remain unknown.