Effect of cyclosporin A on murine natural killer cells.

In mice, cyclosporin A decreased the natural killer cell-enhancing effect of two interferon inducers, infective murine cytomegalovirus and nonreplicating Newcastle disease virus. It also inhibited murine cytomegalovirus replication at doses greater than 20 mg/kg, but it did not significantly inhibit interferon induction by Newcastle disease virus. In cell culture, cyclosporin A had no direct effect on the natural killer activity of spleen mononuclear cells derived from normal or murine cytomegalovirus-infected animals. However, at 50 micrograms/ml it significantly reduced the ability of interferon to enhance the natural killer activity of normal spleen cell suspensions. The inhibitory effect of cyclosporin A on natural killer cell activity in infected mice may be partly explained by its ability to block the action of interferon.