CCL2 and retinal degeneration: To clarify, whether absence of Ccl2 signalling alone might also have a modulatory effect on the RD8 retinal degeneration, we evaluated littermates from the backcrosses that all carried the Crb1RD8/RD8 mutation but were either homozygous wildtype (Ccl2+/+/Crb1RD8/RD8), heterozygous (Ccl2+/−/Crb1RD8/RD8) or homozygous knockout (Ccl2−/−/Crb1RD8/RD8) for the Ccl2 locus (figure 7).