Choroidal neovascularization is inhibited via an intraocular decrease of inflammatory cells in mice lacking complement component C3

In early age-related macular degeneration (AMD), complement component C3 can be observed in drusen, which is the accumulation of material beneath the retinal pigment epithelium. The complement pathways, via the activation of C3, can upregulate the expression of cytokines and their receptors and the recruitment of inflammatory leukocytes, both of which play an important role in the development of choroidal neovascularization (CNV) in exudative AMD. Laser-induced CNV lesions were found to be significantly smaller in C3(-/-) mice than in wild-type mice. By using flow cytometry, we demonstrated that the proportions of intraocular granulocytes, CD11b(+)F4/80(+)Ly6C(hi) and CD11b(+)F4/80(+)Ly6C(lo) cells, were lower in C3(-/-) mice than in wild-type mice as early as day 1 after laser injury, and the proportions of granulocytes and three macrophage/monocyte subsets were significantly lower on day 3. In contrast, C3(-/-) mice had more granulocytes and CD11b(+)F4/80(+)Ly6C(hi) cells in peripheral blood than wild-type mice after injury. Further, the expression levels of Vegfa164 were upregulated in intraocular Ly6C(hi) macrophages/monocytes of C3(-/-) mice, but not as much as in wild-type mice. Collectively, our data demonstrate that despite a more pronounced induction of systemic inflammation, inhibition of complement factor C3 suppresses CNV by decreasing the recruitment of inflammatory cells to the lesion.