Co‐operative effect between insulin‐like growth factor‐1 and interleukin‐2 on DNA synthesis and interleukin‐2 receptor‐α chain expression in human lymphocytes

Recently we demonstrated that IGF‐1 has the same effect on DNA synthesis and G₁‐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‐α chain receptors. Our results showed that the increase in DNA synthesis produced by the addition of IGF‐1 to cells cultured with saturable concentrations of IL‐2, correlated well with an increase in the number of cells expressing IL‐2‐α chain receptor. The effect on both DNA synthesis and IL‐2‐α 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.