Endocrine Abstracts

In the context of the cross-talk between the neuroendocrine and immune systems, it is well known that GH exerts physiological effects in central as well as peripheral compartments of the immune system. GH modulates a variety of thymic functions. For example, GH upregulates proliferation of thymocytes and thymic epithelial cells. Accordingly, GH-transgenic mice, as well as animals and humans treated with exogenous GH, exhibit an enhanced cellularity in the organ. GH also stimulates the secretion of thymic hormones, cytokines and chemokines by the thymic microenvironment, as well as the production of extracellular matrix proteins. These effects lead to an increase in thymocyte migratory responses and intrathymic traffic of developing T cells, including the export of thymocytes from the organ, as ascertained by experimental studies with intrathymic injection of GH in normal mice and with GH-transgenic animals. In addition, GH alters lymphocyte migration in the periphery of the immune system, as assessed by the enhancement of migratory responses of lymphocytes from mesenteric lymph nodes of GH transgenic mice, triggered by the chemokine CXCL12 in conjunction with fibronectin or laminin,compared to lymphocytes from control mice. Since, GH is used as an adjuvant therapeutic agent in immunodeficiencies, including AIDS, the concepts defined herein provide relevant background knowledge for future GH-related immune interventions.