Modulation of humoral immune responses by endogenous opioids.

The effects of opioid agonists and antagonists were investigated on humoral immune mechanisms in mice and rats. Opioid agonists like morphine, Leu-enkephalin, and Met-enkephalin, enhanced antigen-induced histamine release from mixed peritoneal cells of rats in vitro; this enhancement was effectively antagonized by naloxone, an opioid antagonist. Naloxone, per se, decreased anaphylactic mortality in doses of 10 mg/kg, while it increased mortality in a dose of 1 mg/kg. Reduced IgE antibody titer, measured by passive cutaneous anaphylaxis, decreased hemagglutination titer to sheep red blood cells, blocked histamine release from mixed peritoneal cells of rats in vitro induced by antigen, but had no significant effect when histamine release was induced by compound 48/80. Thus, it appears that endogenous opioids are involved in humoral immune responses.