Modulating effect of growth hormone (GH) on PHA-induced lymphocyte proliferation

In order to investigate the ability of growth hormone (GH) to modulate lymphoproliferation, peripheral blood mononuclear cells (PBMC) from healthy adults were stimulated with phytohaemagglutinin (PHA) in the presence of increasing concentrations of pituitary (Crescormon) and biosynthetic (Somatonorm and Genotropin) GH (from 0.425 x 10(3) to 501.5 x 10(3) ng/ml) as well as biosynthetic insulin (rhinsulin, Humulin 1 Eli Lilly: from 0.0012 to 20 U/ml). The results obtained show that low doses of GHs and insulin increase lymphoproliferation. In contrast, high concentrations of GHs (8.5 x 10(3) ng/ml) induce a progressive decrease of PHA-induced lymphoproliferation, while insulin does not. No differences in cell viability were observed with and without GHs. Comparable percentages of lymphocytes bearing interleukin-2 receptor (CD25) and comparable values of interleukin-2 (IL-2) pr oduction were found in all conditions tested. Nevertheless, when exogenous recombinant IL-2 (R IL-2) was added to PHA-induced PBMC cultures with high doses of GH, a reconstitution of lymphoproliferation was observed. Further experiments seem to exclude the presence of suppressor T lymphocyte induction by GH. The present results suggest that hypothesis that high concentrations of GH may interfere with the binding between IL-2 and its membrane receptor on activated lymphocytes.