COOPERATIVE EFFECT BETWEEN INSULIN-LIKE GROWTH-FACTOR-I AND INTERLEUKIN-2 ON DNA-SYNTHESIS AND INTERLEUKIN-2 RECEPTOR-ALPHA CHAIN EXPRESSION IN HUMAN-LYMPHOCYTES

Recently we demonstrated that IGF-1 has the same effect on DNA synthesis and G(1)-phase length during human lymphocyte proliferation as IL-2. In order to determine the link between IGF-1 and IL-2 on lymphocyte proliferation, we tested the ability of these cytokines, alone or in combination, to induce DNA synthesis and increase the number of cells expressing IL-2-alpha chain receptors. Our results showed that the increase in DNA synthesis produced by the addition of ICF-1 to cells cultured with saturable concentrations of IL-2, correlated well with an increase in the number of cells expressing IL-2-alpha chain receptor. The effect on both DNA synthesis and IL-2-alpha chain receptor expression was greater at lower concentrations of PHA. This study suggests that the proliferative effect of IGF-1 might be due to separate stimulation of different cell populations and/or by activation of a tyrosine-kinase signal transduction pathway complementary to the IL-2 activation signal.