Conditions for cytomegalovirus stimulation of lymphocytes.

Lymphocytes from healthy donors or from patients with chronic lymphocytic leukaemia were subjected to live or inactivated cytomegalovirus (CMV) or the mitogen phytohaemagglutinin. No early or late CMV antigens could be demonstrated in the lymphocytes, indicating that neither abortive nor replicative CMV infection takes place. Only cells from CMV antibody-positive leukaemic and non-leukaemic donors were stimulated by CMV to DNA synthesis, with a maximum on day 5. Cells from all individuals responded to phytohaemagglutinin stimulation, the peak of activity occurring on day 3. The stimulation with CMV occurred in T cells and was independent of early CMV antigen production, viral DNA synthesis, or viral replication. CMV is thus not an in vitro lymphocyte mitogen like Epstein-Barr virus but is a very potent antigen for memory T cells.