TREM2 and infection: Interestingly, while microglia downregulated nominally phagocytic genes, Cd68, Mertk and Trem2, following infection, MG4 and MG5 upregulated the TAM receptor Axl (Fig. 3e) which can recognize apoptotic and virus-infected cells expressing phosphatidylserine, potentially enhancing viral clearance [43].