PTX3 Is Located at the Membrane of Late Apoptotic Macrophages and Mediates the Phagocytosis of Macrophages

Apoptotic macrophages are removed by neighboring phagocytes (efferocytosis), which is an important event in advanced atherosclerosis. Recent reports have elucidated some key molecular regulators in efferocytosis including complement C1q, MFGE8, and MERTK. However, it remains unknown whether the long pentraxin 3 (PTX3), which is an important molecule that is involved in apoptotic cell clearance in the immune response, plays a part in efferocytosis during advanced atherosclerosis. In this study, we modeled macrophage apoptosis in advanced plaques by incubating macrophages (peritoneal macrophages isolated from C57 mice) with free cholesterol (free cholesterol-induced apoptotic macrophages, FC-AMs). FC-AMs were added to a monolayer of fresh phagocytes to study the engulfment response. We observed that PTX3 was mainly located at the membrane of late apoptotic macrophages. The anti-PTX3 monoclonal Ab 16B5 inhibited the engulfment of late apoptotic macrophages by phagocytes in a dose-dependent manner (from 14.63% inhibition at 5 μg/ml to 26.19% inhibition at 50 μg/ml). These results suggest that PTX3 located at the membrane of late apoptotic macrophages mediates their phagocytosis by phagocytes in a cell model of advanced atherosclerosis.