CCR2 and neurodegenerative disease: Several groups have demonstrated that resident microglia in the retina show very limited proliferation, supporting the concept of microglial replenishment by blood-derived myeloid cells.43, 44, 45 As a pivotal chemokine for microglia, Ccr2 has revealed its essential pathogenic role in studies of various inflammatory and degenerative diseases.27, 46, 47, 48, 49 In the present study, Ccr2−/− mice with exposure to blue light had significantly reduced infiltration of microglial cells into the retina.