Differentiation between primary and recurrent cytomegalovirus infections.

Two blocking tests were applied simultaneously to detect antibodies to cytomegalovirus (CMV) in human serum specimens. Two different peroxidase-labelled tracers were prepared from human sera taken either early during a primary CMV infection or late after recurrent infection. Sera of acute primary CMV cases effectively competed with the labelled antibodies of the "early" tracer but a rather weak inhibition was observed with the "late" tracer. Sera of cases with recurrent infection strongly inhibited both tracers. Immunoblot experiments were carried out to explain the mechanism of this differential inhibition.