As iMGLs and primary microglia express both C1q and CR3 (CD11b/CD18 dimer), iMGLs were used to assess whether synaptic pruning in human microglia primarily involves this pathway as seen in mice (Chung et al., 2013). Using an additive-free CD11b antibody, iMGL phagocytosis of hS was significantly reduced (−40.0%, ***p<0.0001)(Figure 3H, I). In contrast, an inhibitor of Mertk (UNC569), also implicated in synaptic pruning, only marginally decreased iMGL hS phagocytosis (−12.6%, *p<0.05)(Figure 3H, I). Similar to studies in murine KO models, our data indicates that MERTK plays a minor role in human microglia-mediated synaptic pruning (Chung et al., 2013), whereas C1q/CR3 is integral for microglia-mediated synaptic pruning in humans.
