IGF-I inhibits spontaneous apoptosis in human granulocytes

Granulocytes are key cells in inflammatory processes that are recruited to sites of inflammation by chemoattractants such as IL-8 produced by neutrophils and monocytes. Programmed cell death (apoptosis) of granulocytes and subsequent recognition and phagocytosis by macrophages is a crucial mechanism for resolution of inflammation. Because IGF-I is a potent antiapoptotic factor, we addressed the effects of IGF-I on in vitro apoptosis of human peripheral blood granulocytes. We detected 1390 467 IGF-I receptors with a dissociation constant of 2.3 +/- 0.9 nM on purified granulocytes. Using microscopical analysis, annexin V binding assays to detect relocation of phosphatidylserine to the cell surface, and DNA fragmentation assays, we showed that IGF-I inhibits spontaneous apoptosis of granulocytes in serum-free culture by 32-45%. IGF-I did not modulate the secretion of IL-6, TNFalpha, and IL-8 by granulocytes, but IL-8 secretion by peripheral blood mononuclear cells was enhanced by 40%. These observations indicate that IGF-I may promote granulocyte functions by increasing granulocyte longevity.