CCL2 and retinal degeneration: In order to understand the reported phenotypic discrepancies in the different chemokine knockout mouse models and to study how defects in the two Ccl2 and Cx3cr1 signalling pathways may contribute to the development of the early onset retinal degeneration, we aimed to define primary and secondary pathological events during the age-related progression of the degeneration in CCDKO mice between 2 weeks and 22 months of age [41].