, 2008). Subsequent work showed that blockade of VEGF-A increased leukocyte-endothelial adhesion, which could explain the increase in retinal macrophages following anti-VEGF-A therapy (Walshe et al., 2009). In addition, compensatory elevation in VEGF-A levels following anti-VEGF-A therapy (Willett et al., 2005) might promote inflammatory cell recruitment. These findings raise the following question, the answer to which has important therapeutic implications: What is the ratio of pro- and antiangiogenic macrophages that accumulate after anti-VEGF-A treatment? If the proportion or relative activity of

proangiogenic macrophages increased following anti-VEGF treatments, this finding could explain the tachyphylaxis (desensitization) that occurs with multiple anti-VEGF-A treatments (Forooghian et al., 2009). In that case, the selective inhibition of proangiogenic learn more macrophages would be an appealing adjunct to anti-VEGF therapy. This is in contrast to the

current, Forskolin cost broad-spectrum use of immunosuppression in AMD, which does not target a certain immune cell or subtype. Microglia are another immune cell type that might modulate human CNV pathogenesis. These resident retinal macrophages accumulate in the subretinal space in a CX3CR1-deficient mouse after light-induced and aging models of retinal degeneration; the accumulation of microglia in these mice appears to exacerbate laser-induced CNV ( Combadière et al., 2007). The CX3CR1−/−, CCL2−/−, CCR2−/− mouse models of AMD predominantly exhibit defects in microglia and macrophage function (reviewed in Raoul et al., 2010). When compared to mouse models deficient in either one of these chemokine others receptors, a double-knockout mouse genetically

deficient for both CX3CR1 and CCR2 produced a more penetrant, and earlier-onset, spontaneous phenotype of retinal lesions similar to those seen in dry AMD; also, a subset (15%) of mice spontaneously developed choroidal neovascularization ( Tuo et al., 2007). However, while macrophages accumulate in human CNV membranes, it is not known whether microglia do, too. In the largest histopathologic characterization of microglia in AMD to date, which observed microglia at various stages of AMD pathology, there was a change in microglia morphology, but not number, in AMD compared to nondiseased retinas ( Penfold et al., 1997). The precise functional ramifications of such altered microglia morphology remain to be elucidated. Very recently it has been claimed that many of the early-onset retinal degenerative phenotypes observed in the CX3CR1−/− mice are attributable to the fact that these mice were generated on the C57BL/6N background, which contains the rd8 retinal degeneration mutation of the Crb1 gene ( Mattapallil et al., 2012). However, the CCL2−/− and CCR2−/− mice were generated on the C57BL/6J background, which does not contain the rd8 mutation, and develop retinal findings many months later than rd8 mice ( Ambati et al., 2003b).