Urticaria associated with acute viral hepatitis type B: studies of pathogenesis.

To determine whether skin deposition of circulating immune complexes contributes to prodromal urticaria of acute hepatitis B, we studied two patients with hepatitis B who presented with urticaria and fever. During the urticarial prodrome but not thereafter, we found activation of both classic and alternative complement pathways. Hepatitis B surface antigen (HBsAg)-antibody complexes were identified (by electron microscopy) in cryoprecipitates from both patients and IgG (by immunodiffusion) in cryoprecipitates of one patient during urticaria. Light and electron microscopy of involved urticarial skin revealed necrotizing venulitis in both patients. Immunofluorescence microscopy showed fibrin within involved cutaneous vessel walls in one patient and C3, IgM, and HBsAg, which were not detected in simultaneously obtained uninvolved skin, in both patients. Our findings suggest that deposition of circulating immune complexes containing HBsAg is important in the pathogenesis of urticaria associated with acute hepatitis B virus infection.