Phenotypic analysis of splenocyte subsets following acute morphine treatment in the rat

Prior studies by our laboratory demonstrated that a single injection of mor phine produces dose-dependent, naltrexone-reversible, suppressive effects i n assays of mitogen-stimulated lymphocyte proliferation and natural killer (NK) cell cytotoxicity in the spleen. The present study used how cytometry to assess directly whether acute morphine treatment produces these immune a lterations by altering the leukocyte composition of the spleen. In agreemen t with our previous findings, morphine suppressed the concanavalin A-stimul ated proliferation of T cells, lipopolysaccharide-stimulated proliferation of B cells, and NK cell cytotoxicity in the spleen. However, the same morph ine treatment protocol did not alter the total number of splenic leukocytes , the percentage of live splenic leukocytes (as assessed by forward-scatter versus side-scatter histograms), or the relative number of CD4(+)CD3(+) T cells, CD8(+)CD3(+) T cells, CD45RA/B+ B cells, NKR-P1A(hi)CD3(-) NK cells, NKR-P1A(lo)CD3(+) T cells, CD11b/c(+)HIS48(-) monocytes/macrophages, or CD 11b/c(+)HIS48(+) granulocytes in the spleen. These findings indicate that t he effects of a single sc dose of morphine on functional measures of immune status in the spleen do not result from a redistribution of splenic leukoc ytes; instead, morphine's effects likely result from direct alterations in leukocyte activities. (C) 1999 Academic Press.