Demonstration of receptors for insulin-like growth factor-II on human T-lymphocytes.

Primary human T-lymphocytes that have been mitogen activated in chemically defined medium demonstrate cell surface receptor for insulin-like growth factor-II (IGF-II). In contrast resting T-lymphocytes demonstrate little or no IGF-II receptor. Receptors appear within 24 hours of mitogen activation with maximal binding occurring at 72 hours. After this point IGF-II binding declines. Receptor binding of IGF-II to T-lymphocytes does not show a sharp pH dependence but is maximal above pH 7. Insulin does not compete for IGF-II binding sites and proinsulin competes only weakly, suggesting that this is a type 2 IGF receptor and not an insulin receptor. Furthermore, anti-insulin antibodies do not inhibit IGF-II from binding to activated T-lymphocytes indicating divergent binding domains on the two peptide hormones. IGF-II demonstrates stimulating action on T-lymphocyte proliferation probably mediated by binding of IGF-II to this receptor.