Morphine alters macrophage and lymphocyte populations in the spleen and peritoneal cavity.

We have previously shown that subcutaneous implantation of a 75 mg morphine pellet results in suppression of the ability of murine splenocytes to mount an antibody response to sheep red blood cells, due in part to a reduction of macrophage function. The present studies used flow cytometry to examine whether the decrement in macrophage function in the spleens of morphine-treated mice results from a reduction in macrophage numbers. Parallel analysis was carried out on non-elicited peritoneal cells. In the spleen, morphine resulted in a reduction in the relative proportion of macrophages and B-cells, with a concomitant increase in the proportion of T-cells. Alteration in the ratio of CD4+ to CD8+ T-cells was not observed. In contrast, in the peritoneal cavity, morphine increased the number of macrophages and reduced the number of B-cells. Naltrexone blocked all of the changes in cellular composition. These results support the conclusion that an important mechanism in the immunosuppression seen in the spleens of mice implanted with morphine pellets is a differential reduction in the number of macrophages and B-cells as compared with T-cells. Further, these studies show that subsets of cells of the immune system are differentially affected by morphine in different anatomical compartments.