To control for genetic background variability, which might account for some of the reported phenotypic variability in retinal degenerations of chemokine knockout mice, we established single Ccl2, single Cx3cr1 and double Ccl2/Cx3cr1 knockout mice from the original CCDKO mouse line by backcrossing with C57Bl/6 mice. The gene discussed is CX3CR1; the disease is retinal degeneration.