Enkephalins and immunity. II: In vivo modulation of cell-mediated immunity.

Body, thymus, and spleen weights, and cellular makeup of lymphoid tissues of rat were not affected to a great extent by intraperitoneal injections of met-enkephalin, leu-enkephalin, or naloxone. However, enkephalins induced a diminution of peripheral blood leukocytes and lymphocytes. In addition, met-enkephalin depleted the population of T4 helper/inducer lymphocytes. On the other hand, there was an increase of blood leukocytes and lymphocytes in naloxone-treated animals. Arthus and delayed skin hypersensitivity reactions to bovine serum albumin and old tuberculin were sharply reduced in enkephalin-treated rats. Rejection of allogenic thyroid graft implanted under the renal capsule was considerably delayed by repeated injections of enkephalins. Mesenteric mast cell degranulation in rats sensitized to ovalbumin and injected with a shocking dose of antigen was less pronounced after treatment with enkephalins. These results show that enkephalins, in dosage levels of 5 mg/kg b.w., exert a suppressive influence on cell-mediated immune reactions. Other experiments from our laboratory, reported in a companion paper in this volume, suggest that much lower doses may have opposite (immunoenhancing) effects.