Complement-Requiring Neutralizing Antibodies in Hyperimmune Sera to Human Cytomegaloviruses

Abstract

High-titered antisera to two strains of human (C87 and AD169) and two strains of monkey (GR2598 and GR2757) cytomegaloviruses (CMV) were prepared in primates hand-reared in captivity and free of pre-existing antibodies. Unlike monkey CMV, which elicited the production of complement-independent neutralizing (CIN) antibodies, hyperimmune sera to the two human strains were found to contain chiefly complement-requiring neutralizing (CRN) antibodies. The CRN antibodies elicited by human CMV were specific for the immunizing virus and were not directed to host-cell components. Treatment of whole serum with 2-mercaptoethanol indicated that 7S antibodies comprised the major population of CRN antibody activity in both early and late anti-human CMV sera. Preparations of highly purified early and late IgG (6.4S) and IgM (18.6S) anti-human CMV immunoglobulins all required complement for neutralization. The complement dependency of late IgG appears to be a phenomenon unique for antisera against human CMV. Cross-neutralization tests indicated a two-way cross between the two human viruses and a two-way cross between the two monkey viruses with negligible interspecies reactivity.