IgA1 is the major IgA subclass in cutaneous blood vessels in Henoch-Schönlein purpura.

Henoch-Schönlein purpura (HSP) is characterized by palpable purpura predominantly involving the lower extremities. On direct immunofluorescence IgA can be seen deposited in the blood vessel walls of the superficial dermis. The subclass distribution of antibodies to this IgA was studied in the biopsies of 28 patients with HSP by direct immunofluorescence using anti-IgA1 and anti-IgA2 specific monoclonal antibodies. All 28 patients' biopsies demonstrated deposition of IgA1 while only one patient had IgA2 deposition. Positive and negative controls stained appropriately. This demonstrates that IgA1 is the dominant IgA subclass found in the skin in Henoch-Schönlein purpura.