TYPE-I INSULIN-LIKE GROWTH-FACTOR RECEPTOR EXPRESSION IN DIFFERENT DEVELOPMENTAL STAGES OF HUMAN THYMOCYTES

Insulin-like growth factor-I (IGF-I) has been implicated in playing a regulatory role in T cell development and in T cell function. We demonstrate the presence of type I IGF receptors on human thymocytes using radioligand binding assays and flowcytometric analysis. The relative potencies of IGF-I, IGF-II and insulin for competition with I-125-IGF-I indicate the presence of type I IGF receptors. Scatchard analysis revealed that the average number of receptors per thymocyte is 257 +/- 28 with a K-d of 0.12 +/- 0.01. With multicolour flowcytometry using a type I IGF receptor specific monoclonal antibody (alpha IR3), we show that CD4(-)CD8(-) cells express 3-4 times more receptors per cell as compared with CD4(+)CD8(+), CD4(+)CD8(-) and CD4(-)CD8(+) cells. IGF-I directly stimulated DNA synthesis of thymocytes and potentiated DNA synthesis in mitogen-activated thymocytes. These results indicate that IGF-I can influence T cell development in humans at the level of the thymus.