The resolution of inflammation is a dynamically regulated process that may be subverted in many pathological conditions. Macrophage (Mphi) phagocytic clearance of apoptotic leukocytes plays an important role in the resolution of inflammation as this process prevents the exposure of tissues at the inflammatory site to the noxious contents of lytic cells. It is increasingly appreciated that endogenously produced mediators, such as lipoxins, act as potent regulators (nanomolar range) of the phagocytic clearance of apoptotic cells. In this study, we have investigated the intriguing possibility that apoptotic cells release signals that promote their clearance by phagocytes. We report that conditioned medium from apoptotic human polymorphonuclear neutrophils (PMN), Jurkat T lymphocytes, and human mesangial cells promote phagocytosis of apoptotic PMN by Mphi and THP-1 cells differentiated to a Mphi-like phenotype. This prophagocytic activity appears to be dose dependent, sensitive to the caspase inhibitor zVAD-fmk, and is associated with actin rearrangement and release of TGF-beta1, but not IL-8. The prophagocytic effect can be blocked by the formyl peptide receptor antagonist Boc2, suggesting that the prophagocytic factor(s) may interact with the lipoxin A(4) receptor, FPRL-1. Using nanoelectrospray liquid chromatography mass spectrometry and immunodepletion and immunoneutralization studies, we have ascertained that annexin-1 and peptide derivatives are putative prophagocytic factors released by apoptotic cells that promote phagocytosis of apoptotic PMN by M[phi] and differentiated THP-1 cells. These data highlight the role of annexin-1 and peptide derivatives in promoting the resolution of inflammation and expand on the therapeutic anti-inflammatory potential of annexin-1.