Enhanced immune response late in primary cytomegalovirus infection of mice.

Murine cytomegalovirus (MCMV) infection has been previously shown to depress humoral and cell-mediated functions to non-MCMV antigens. In this report we show that in C3D2 mice undergoing nonlethal primary infection the depressed anti-sheep RBC plaque-forming cell (PFC) response is followed by an enhanced PFC response. Infected mice often generated twice the number of PFC per spleen than that of control mice. Total numbers of spleen cells as well as the recovery of virus from spleens of infected mice did not distinguish the depressed from the enhanced phase of the response. Investigation of the kinetics of the response revealed a defect in shutdown regulation. This enhanced PFC response during primary MCMV infection was not reflected in measurements of serum hemagglutinin. These findings suggest that MCMV induces an impairment of immunoregulation.