Effect of retinoic acid on the spontaneous and interferon-induced activity of human natural killer cells.

Non-toxic concentrations of retinoic acid (RA) inhibited the spontaneous activity of human natural killer (NK) cells. RA also inhibited the activation of human NK cells by treatment with partially purified human leukocyte interferon (HulFN alpha) or with inducers of IFN alpha and IFN gamma. Full expression of the inhibitory action required prolonged exposure of human peripheral blood leukocytes to RA. Implications of these findings for the use of retinoids in the treatment of human malignancies are discussed.