title: Natural cell-mediated cytotoxicity in rats. III. Effects of immunopharmacologic treatments on natural reactivity and on reactivity augmented by polyinosinic-polycytidylic acid.
abstract: Treatment of rats with high doses of hydrocortisone, X-irradiation, or cyclophosphamide had a suppressive effect on natural cytotoxicity in vivo. However, when rats were given poly I:C after any of these agents, the levels of NK activity were similar to those in normal rats which had been given poly I:C alone. To explain these findings, we have postulated that a population of pre-NK cells, resistant to hydrocortisone, cyclophosphamide and X-irradiation was induced by poly I:C to become cytotoxic NK cells. Treatment of rats with silica, in doses that had no effect on proliferative responses of host lymphocytes to Con A in vitro, sharply diminished NK activity. With this agent, the boosting effect of poly I:C, although still detectable, was diminished. Since there is little if any indication that NK cells are phagocytic, these data suggest that phagocytes may play a role in maintaining high levels of NK activity in vivo and, further, may be involved in the mechanism by which natural cytotoxicity is boosted by poly I:C. Adult thymectomized rats had easily detectable levels of natural reactivity and the response to poly I:C was unimpaired, indicating a lack of thymic dependence for boosting as well as for spontaneous levels of NK activity.
mesh_terms: D000818:Animals; D000920:Antibody-Dependent Cell Cytotoxicity / Q000187:drug effects / Q000528:radiation effects; D003520:Cyclophosphamide / Q000494:pharmacology; D003602:Cytotoxicity, Immunologic / Q000187:drug effects* / Q000528:radiation effects; D006854:Hydrocortisone / Q000494:pharmacology; D007117:Immunization, Secondary; D007165:Immunosuppression Therapy; D007694:Killer Cells, Natural / Q000187:drug effects / Q000276:immunology*; D008297:Male; D008934:Mitogens / Q000494:pharmacology; D011069:Poly I / Q000494:pharmacology*; D011131:Polyribonucleotides / Q000494:pharmacology*; D051381:Rats; D012822:Silicon Dioxide / Q000494:pharmacology; D013934:Thymectomy
chemical_list: D008934:Mitogens; D011131:Polyribonucleotides; D011069:Poly I; D012822:Silicon Dioxide; D003520:Cyclophosphamide; D006854:Hydrocortisone