Effect of isoprinosine on natural killer cell activity of blood mononuclear cells in vitro and in vivo.

Addition of isoprinosine to cultures of blood mononuclear cells was shown to inhibit natural killer (NK) cell activity against the K562 myeloid cells and melanoma cells. This appeared to be due to inhibitory influences of monocytes in that after removal of adherent cells isoprinosine appeared to stimulate NK activity. Similar effects were noted on T cells separated by E rosette procedures. Administration of isoprinosine in vivo had variable effects on NK activity during drug administration but there was a significant increase in NK activity 3 days after cessation of the drug. These changes in NK activity may reflect different threshold levels of the drug on suppressor and NK cell populations and the relative proportions of different lymphocyte populations in individual subjects. Further studies with a wider range of drug doses and more frequent monitoring of responses are required to further evaluate the effect of isoprinosine on NK activity.