MERTK and atherosclerosis: The switch from an M2 to an M1 promoting environment during atherosclerosis progression may impede apoptotic cell clearance as M2 cells have greater capacity for efferocytosis [90] (Figure 1); this is through various pathways such as the expression of MR [91] and up-regulation of MER proto-oncogene tryosine kinase (MERTK) (on M2c), which is not induced on M1 macrophages [49],[92].