Complement activation molecule C5a appears to play role in inflammation

The authors conducted this laboratory study to learn more about the effects of the complement activation molecule C5a on retinal pigment epithelial (RPE) cells and peripheral blood mononuclear cells (PBMCs). The results, which were published in December in the British Journal of Ophthalmology, suggest that C5a helps to produce a pro-inflammatory intraocular environment that may contribute to local inflammation. This work adds key mechanistic data implicating the interaction of the complement system, RPE cells and PBMCs in the pathogenesis of age-related macular degeneration (AMD).

The authors investigated the role of C5a in modulating responses in arising retinal pigment epithelial cell line-19 (ARPE-19) and PBMCs isolated from healthy adult volunteers. Western blot, real-time PCR and cell surface receptor staining were used to detect C5a receptor expression. Real-time PCR (RT-PCR) was used to detect cytokine mRNA expression. A thiazolyl blue tetrazolium bromide assay detected cell viability. Cells were stained with Annexin V and 7-aminoactinomycin D for an apoptosis assay. Cell proliferation was measured using a tritiated thymidine incorporation assay.

C5a receptors were detected in ARPE-19 cells and C5a receptor mRNA expression (as measured by RT-PCR). Cell surface expression (flow cytometry/immunohistochemistry) was increased by C5a and the pro-inflammatory cytokines Il-1b, TNF-a and IFN-g. Treatment of ARPE-19 cells with C5a decreased production of transforming growth factor (TGF)-β2, a key anti-inflammatory cytokine. Also, C5a reduced ARPE-19 mitochondrial activity without inducing apoptosis.

The results indicate that C5a favors T cell proliferation and the secretion of proinflammatory cytokines, which in turn increase the number of C5a receptors on RPE cells, rendering these cells more sensitive to the detrimental effects of C5a. The findings also show that a close, reciprocal interaction between the innate immune system and the adaptive immune system may be involved in the development of intraocular inflammatory diseases. The authors say the results suggest that new therapeutic strategies can be developed to disrupt the innate-adaptive circuitry, and one possible approach may involve targeting C5a.