Abstract
Sera from infectious mononucleosis patients aged 2 to 35 years and from normal subjects aged 11 to 35 years were examined for the presence of antibody to the EB virus capsid antigen (VCA) in the indirect immunofluorescence test, and for the presence of antibody reactive with the soluble (S) antigen of lymphoblastoid cell lines in the complement‐fixation test. Sera from all infectious mononucleosis patients taken either in the acute stage of the disease or up to 9 years after its onset contained VCA antibody. The sera taken in the acute stage of the disease were free of S antibody; out of 97 sera investigated only one was weakly reactive. Only one of the seven sera taken 4 to 5 months after the onset of the disease contained S antibody. After the 7th month following onset, the majority of the subjects possessed S antibody. These data indicate that the S antibody appears much later in the course of EB virus infection than the VCA antibody. The predominant majority of sera from subjects with no history of the disease possessed VCA antibody; most of these also possessed S antibody. The incidence of S antibody in these subjects and those who had been suffering from infectious mononucleosis 1 to 9 years previously were comparable.