Augmentation of natural cytotoxicity by leucine enkephalin in cultured peripheral blood mononuclear cells from patients infected with human immunodeficiency virus.

Natural Killer (NK) activity of lymphocytes from acquired immunodeficiency syndrome (AIDS) patients is frequently below normal and declines as disease progresses. We studied the potential of leucine enkephalin (leu-enkephalin) to restore this immune parameter by incubating nylon wool nonadherent mononuclear cells from 14 patients in the presence or absence of leu-enkephalin, and measuring NK cytolysis in a standard 51Cr release assay. The NK activity of human immunodeficiency virus antibody positive (HIV+) individuals with some remaining NK lytic ability was significantly augmented by leu-enkephalin concentrations of 10(-10) and 10(-8) M (n = 7). HIV+ patients with no measurable basal level of NK activity (n = 3) were not responsive to stimulation with leu-enkephalin. Human immunodeficiency virus antibody negative (HIV-) individuals (n = 4) responded in a pattern similar to normals. In addition, naloxone, an antagonist of alkaloid and peptide opiates including leu-enkephalin, displayed the properties of an antagonist/agonist, reflecting the immunoregulatory capacities of the endogenous opiate system.