Inhibition of mouse natural killer activity by cyclosporin A

Cyclosporin A(CSA), administered in vivo or in vitro, inhibited the spontaneous cytotoxicity of C57BL/6 and NZB/WF1 mouse spleen cells against YAC and K562 target cells in a 4 hr 51Cr release assay. Inhibition of natural killing (NK) by CSA occurred rapidly, was dose-dependent, and did not require the presence of T cells, B cells or macrophages. CSA depressed NK activity by direct interaction with NK cells. There was no evidence that inhibition of NK by CSA was mediated through suppressor cells.