Reversibility of morphine effects on phagocytosis by murine macrophages

Abstract

Proneness of addicts to infections may be partially due to opiate effects on immune cells. We find that acute morphine inhibits phagocytosis in murine peritoneal macrophages in vitro with apparent desensitization at high concentrations, whereas chronic exposure results in a state akin to tolerance/dependence where macrophages seem to require morphine to phagocytize at a control level. However, both putative desensitization and tolerance/dependence are reversible, since drug re-addition several hours after withdrawal results in inhibition, as in acute exposure. This shows that opiate effects on immune cells are variably related to the experimental context in which they are administered, which is of relevance for understanding their potential role in immunosuppression.