Growth Hormone Stimulates the Selective Trafficking of Thymic CD4+CD8– Emigrants to Peripheral Lymphoid Organs

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Abstract
Growth hormone (GH) has been shown to stimulate T cell development. However, its mechanisms of action on the peripheral T cell pool remain unknown. To address this question, intrathymic injection of GH in combination with fluorescein isothiocyanate (FITC) was used to assess the effects of GH on T cell trafficking from the thymus to the periphery. GH promoted a significant increase in the percentage and differential distribution of thymic CD4+CD8–FITC+ cells in secondary lymphoid organs. A significantly higher percentage of CD4+CD8–FITC+ cells was observed in the lymph nodes, while a relative decrease of these cells was found in the spleen. Moreover, we verified that GH treatment resulted in increased numbers of CD62L+CD4+CD8–FITC+ T cells in the lymph nodes, while the same treatment resulted in a decline in the percentage of VLA-6+CD4+CD8–FITC+ T cells in the spleen. Together, these findings suggest that GH is a potent immunoregulatory molecule which selectively stimulates the preferential homing of CD4+CD8– thymic emigrants to the subcutaneous lymph nodes possibly via the differential expression of CD62L and VLA-6.