Tagging Of Apoptotic Cells By The β-chemokine CCL5/RANTES Stimulates Phagocytosis By Macrophages

RANTES (regulated upon activation normal T cell expressed and secreted; CCL5) is a member of the -CC- subfamily of chemokines, mainly generated by CD8+ T cells. When RANTES was first identified, it appeared to be a typical chemokine in that it was able to recruit leukocytes to sites of inflammation. In the course of studies that explored the potential use of RANTES in HIV therapy, additional and challenging features of RANTES biology have emerged. Recent studies show that CD8+ T cells contact with tumor cell targets elicits a vectorial release of the chemokine CCL5/RANTES resulting in the selective deposition of RANTES on target cells. However, the physiological significance of this process is still unknown.To test the effect of RANTES on inflammation and immune regulation, we employed the mouse thioglycollate-elicited peritonitis model to determine by fluorescence-activated cell sorting (FACS) if RANTES stimulates M phagocytosis of apoptotic cells. Out data revealed that RANTES on the surface of apoptotic cells enhances their phagocytosis by macrophages. Using recombinant techniques, RANTES wereconverted to GPI-anchored forms. The role of RANTES aggregation on the enhanced phagocytosis was then investigated using RANTES and nonaggregating variants produced by means of single or multiple amino acid substitutions, enabling comparison of aggregated, tetrameric, and dimeric RANTES forms. Oligomerization of RANTES at least at the level of a tetramer is required for this effect. To evaluate the potential role of CCR1 or CCR5 on this process, the receptors were blocked by either BX 471 a small molecule antagonist of CCR1, or a blocking antibody to murine CCR5. The enhanced phagocytosis is mediated through chemokine receptor CCR1. Furthermore, this effect appears unique to RANTES as the related p-chemokines MIP-1 a , MIP-1B and MCP-1 do not significantly affect uptake.This study highlights a novel biologic activity for RANTES, a member of the p-chemokine family best known for its ability to induce directional cellular recruitment. By moderation of phagocytosis, RANTES may enhance removal of tumors and impact immune regulation in diverse biologic circumstances.