Human lymphocyte growth hormone stimulates interferon gamma production and is inhibited by cortisol and norepinephrine.

Lymphocyte growth hormone (L-GH) is distributed throughout the human immune system; however, its biologic role has not been defined. In order to clarify this issue, we determined if Candida, commonly used as a recall antigen, and IL-12, an important monocyte cytokine that stimulates the TH1 cytokine pathway, could stimulate L-GH mRNA synthesis in cultured human peripheral blood mononuclear cells (PBMCs). Both Candida and IL-12 produced significant (p<0.01) stimulation of L-GH mRNA synthesis and the TH1 cytokine, gamma interferon (IFN-gamma). These effects on IFN-gamma production were significantly (p<0.001) inhibited by a GH antagonist, suggesting that L-GH was acting by an autocrine or paracrine mechanism to enhance IFN-gamma production in these serum-free cultured cells. Concentrations of norepinephrine and cortisol achievable in humans during stress were able to significantly (p<0.001) decrease L-GH synthesis in the PBMCs. They also diminished IFN-gamma significantly (p<0.001), but not the TH2 cytokine, IL-10, in the supernatants of the cultured PBMLs. These studies suggest that L-GH plays a role in cellular immune function mediated via the TH-1 pathway.