Quantitative evaluation of Epstein-Barr-virus-infected mononuclear peripheral blood leukocytes in infectious mononucleosis.

We devised a quantitative assay for Epstein-Barr-virus-infected mononuclear leukocytes (virocytes) to determine their prevalence in the blood of patients with acute-phase and convalescent-phase infectious mononucleosis and in healthy Epstein-Barr-virus-seropositive controls. Mononuclear peripheral blood leukocyte suspensions were tested for virus-determined cytoproliferative activity by cocultivation with human cord-cell indicator cultures. The highest levels of virocytes among circulating mononuclear leukocytes were found in the early acute phase of infectious mononucleosis (up to 0.05 per cent). Virocytemia decreased to levels comparable with those of healthy controls (less than 0.00001 per cent) by the third month after onset of infectious mononucleosis. These findings provide a quantitative profile of the course of the infection at cellular level and support existing evidence of the efficiency of immune control mechanisms in limiting Epstein-Barr-virus infection during the course of infectious mononucleosis.