Multiple interactions between murine cytomegalovirus and mouse lymphoid cells in vitro

Swiss white mice and C3H/HeJ mice were used occasionally. It was shown that in vitro infection resulted in the formation of infectious centers in only a small percentage of the spleen cell population even at high multiplicities of infection, when a proportionately higher number of virus particles were being taken up by the cells. Virus could be rescued from some of these infected cells by co-cultivation with susceptible mouse embryo fibroblasts, and the emerging infectious virus particles were detectable 40-50 hours after the start of co-cultivation. It appeared that allogeneic stimulation was not essential to virus rescue in our in vitro system, for both syngeneic and allogeneic mouse embryo fibroblasts were equally efficient in effecting virus reactivation from infected spleen cells. A fraction of the infected spleen cells was capable of supporting spontaneous MCMV replication. Such replication was not affected by incubation with the mitogens Con A or LPS prior to or after infection with the virus. However, the presence of an increased number of activated T cells due to Con A stimulation possibly inhibited virus replication to a certain extent. Virus replication was also reduced in the absence of some heat-labile factor in the fetal calf serum. Cell separation techniques such as nylon wool column adherence, plastic adherence, anti-serum treatment and y-xay irradiation, showed that macrophage-like cells were probably involved in harboring MCMV in a latent state although spontaneous replication did take place to a limited extent in such cells. Another cell fraction, with B-cell-like properties, was capable of supporting spontaneous MCMV replication. Another effect of in vitro MCMV infection on spleen cells was their suppressive effect on the mitogenic responses of such cells. Preliminary evidence suggested that the defective con A response might be mediated by macrophages exposed to MCMV. Moreover, the immunosuppressive effect could only be observed after exposure to infectious virus particles, and the degree of suppression of mitogen responses could be increased by using higher multiplicities of infection. In certain cases, a slight stimulatory effect on the spleen cells was observed about 30 hours after infection. In summary, the spleen cell population contained cell fractions that were capable of harboring MCMV in a latent state and supporting spontaneous viral replication. In addition, the mitogenic responses of infected cells were impaired.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat