Variable effect of encephalomyocarditis virus on host defense mechanisms.

A number of viruses have been shown to suppress a variety of host defense mechanisms. To further define the effect of a viral infection on host resistance, a number of parameters were examined during the course of a lethal encephalomyocarditis virus infection of mice. The peripheral lymphocyte count, the induction of interferon in spleen cells by Newcastle disease virus, and the proportion of B cells in the spleen were all decreased or suppressed. In contrast, the responsiveness of spleen lymphocytes to phytohemagglutinin, the delayed-type skin hypersensitivity to dinitrofluorobenzene, and the proportion of T cells in the spleen remained normal. These results indicate that a viral infection may have divergent effects on different parameters of host resistance and emphasize the need to examine several functions before drawing conclusions about the effect of viral infections on host defense mechanisms.