Immunoglobulin A antibody to Epstein-Barr viral antigens and prognosis in nasopharyngeal carcinoma.

IgA immunoglobulin fractions containing antibodies to Epstein-Barr virus (EBV)-induced membrane antigens were isolated from the sera of two patients with nasopharyngeal carcinoma (NPC), from one non-NPC patient, and from three persons with sera negative for IgA antibodies. IgA antibodies were not cytotoxic against cells expressing EBV-induced membrane antigens in the antibody-dependent cellular cytotoxicity (ADCC) assay. However, IgA antibodies blocked IgG-mediated ADCC, which indicated that these antibodies could serve as a blocking "factor" in patients with disease and, therefore, were potentially detrimental to the host.