Insulin-Like Growth Factor I Promotes Maturation and Inhibits Apoptosis of Immature Cord Blood Monocyte-Derived Dendritic Cells through MEK and PI 3-Kinase Pathways

IGF-I has profound effects on the immune system. We previously reported that IGF-I promoted cord blood (CB)-naïve T-cell maturation and now show that IGF-I promoted maturation of CB monocyte-derived dendritic cells (DC) with up-regulation of CD83, CD86, CD40, and major histocompatibility complex (MHC) class II molecules, and down-regulation of mannose receptor. Furthermore, IGF-I inhibited apoptosis of CB DC and increased the production of tumor necrosis factor α (TNF-α). These effects were blocked by specific mitogen-activated protein kinase kinase (MEK) inhibitor (PD98059) and phosphoinositol 3-kinase inhibitor (LY294002). PD98059 partially inhibited the IGF-I-induced up-regulation of MHC class II. In contrast, LY294002 was additive in the IGF-I-induced up-regulation of MHC class II. Moreover, LY294002 significantly increased the percentage of late apoptotic cells in CB. These results imply the involvement of different pathways for the differential regulation of co-stimulatory molecule expression and apoptosis. The addition of anti-TNF-α did not neutralize the effects of IGF-I on CB DC maturation and apoptosis. On the contrary, neutralizing TNF-α significantly increased the IGF-I-induced up-regulation of CD83 and CD40. We conclude that IGF-I has maturation and survival effects on CB DC. These effects are mediated through both MEK and PI 3-kinase pathways but not through the IGF-I induction of TNF-α production by the DC.