In vivo administration of GM-CSF promotes the clearance of apoptotic cells: effects on monocytes and polymorphonuclear leukocytes

The clearance of apoptotic cells is crucial to avoid chronic inflammation a nd autoimmunity, Little is known about the factors that regulate it in vivo . We show that granulocyte-macrophage colony-stimulating factor (GM-CSF) ad ministration to carcinoma patients confers to their leukocytes a significan tly higher ability to phagocytose apoptotic cells than before (P < 0.005), GM-CSF increased the concentration of monocytes and polymorphonuclear leuko cytes in the peripheral blood and activated circulating polymorphonuclear l eukocytes, Both effects abated early after treatment, whereas phagocytosis of apoptotic cells was still significantly higher after 18 days compared wi th basal values (P < 0.005 and P < 0.025 for monocytes and polymorphonuclea r leukocytes, respectively). On in vitro phagocytosis of apoptotic cells mo nocytes, but not polymorphonuclear leukocytes, up-regulated MHC class II me mbrane expression, These findings are consistent with the possibility that GM-CSF endows both scavenger and antigen-presenting leukocytes with the abi lity to internalize apoptotic turner cells.