Immunologic studies in subjects with a serum sickness-like illness after immunization with human diploid cell rabies vaccine.

Ten patients developing a serum sickness-like hypersensitivity reaction to human diploid cell rabies vaccine were studied and compared with control subjects matched for previous vaccination history and level of rabies virus-specific IgG response to immunization. The clinical reaction consisted of delayed onset, generalized urticaria, and angioedema, with some arthralgias. Skin biopsy specimens demonstrated a leukocytoclastic vasculitis. Individuals reacting to the vaccine possessed IgE antibodies to human diploid cell rabies vaccine, to mock vaccine lacking viral antigen, and to fetal calf serum (FCS), a vaccine trace contaminant. Increased levels of IgG antibodies to FCS, mock vaccine, and beta-propiolactone-modified FCS, and human serum albumin were also found. Such humoral responses to vaccine components other than rabies virus might be responsible for the hypersensitivity reactions developing after rabies vaccination.