Interactions between thymic endothelial cells and thymocytes are influenced by growth hormone.

Growth hormone (GH), in addition to its classic actions on growth and metabolism in the body, exerts pleiotropic effects on the immune system, particularly on the thymus. The aim of this study was to evaluate the influence of GH on the interactions between mature thymocytes and the thymic endothelium involved in the migratory process. To this end, fresh thymocytes (C57BL/6 mice) and the thymic endothelial cell line (tEnd.1) were used. In the cell adhesion assay, the GH-treated thymocytes adhered more to tEnd.1 cells. Additionally, there was an improvement in the deposition of fibronectin by tEnd.1 cells when co-cultured with GH-pre-treated thymocytes. Furthermore, GH induced thymocyte F-actin polymerization. In the transendothelial migration assay, a large number of GH-treated thymocytes, mainly the CD4^-CD8⁺ subset, migrated towards the endothelium under the stimulus of insulin-like growth factor 1. In conclusion, we demonstrated the positive actions of GH in thymocyte/thymic endothelium interactions, including transendothelial migration.