Endogenous opioids and immune responses: an experimental study

Possible involvement of endogenous opioids in humoral immune responses has been explored in the experimental animals. Opioid agonists like morphine and leu-enkephalin significantly enhanced antigen-induced histamine release from the peritoneal mast cells of sensitised rats in vitro; this was effectively antagonised by naloxone. Naloxone itself inhibited antigen-induced histamine release. Animals were effectively protected against anaphylactic shock by naloxone which also antagonised morphine-induced increase in anaphylactic mortality. Naloxone reduced haemagglutination titre to sheep red blood cells and IgE antibody titre as measured by passive cutaneous anaphylaxis. Thus, endogenous opioids appear to be involved in the mediation of humoral immune responses. They seem to act at various steps in the immune mechanism viz (i) antibody production and (ii) release of mediators of hypersensitivity reactions.