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Age-related macular degeneration is a leading form of blindness in Western countries and is associated with a common SNP (rs 1061170/Y402H) in the Factor H gene, which encodes the two complement inhibitors Factor H and FHL1. However, the functional consequences of this Tyr(402) His exchange in domain 7 are not precisely defined. In this study, we show that the Tyr(402) His sequence variation affects Factor H surface recruitment by monomeric C-reactive protein (mCRP) to specific patches on the surface of necrotic retinal pigment epithelial cells. Enhanced attachment of the protective Tyr(402) variants of both Factor H and FHL1 by mCRP results in more efficient complement control and further provides an anti-inflammatory environment. In addition, we demonstrate that mCRP is generated on the surface of necrotic retinal pigment epithelial cells and that this newly formed mCRP colocalizes with the cell damage marker annexin V. Bound to the cell surface, Factor H-mCRP complexes allow complement inactivation and reduce the release of the proinflammatory cytokine TNF-α. This mCRP-mediated complement inhibitory and anti-inflammatory activity at necrotic membrane lesions is affected by residue 402 of Factor H and defines a new role for mCRP, for Factor H, and also for the mCRP-Factor H complex. The increased protective capacity of the Tyr(402) Factor H variant allows better and more efficient clearance and removal of cellular debris and reduces inflammation and pathology.

Human complement factor H (CFH), a central complement control protein, is a member of the regulators of complement activation family. Recent studies suggested that CFH may play a key role in the resistance of complement-mediated lysis in various cancer cells. In this study, we investigated the role of CFH in human lung cancer. Expression of CFH was analyzed in lung cancer cell lines by RT-PCR, Western blotting and immunofluorescence. In primary lung tumors, the protein expression of CFH was evaluated by immunohistochemistry (IHC) on tissue microarray (TMA). Binding of CFH to lung cancer cells was detected by flow cytometry. mRNA expression of CFH was detected in 6 out of 10 non-small cell lung cancer (NSCLC) cell lines, but in none of the small cell lung cancer (SCLC) cell lines. In line with Western blotting, immunofluorescence analysis demonstrated CFH protein expression in 3 NSCLC cell lines, and the immunoreaction was mainly associated with cell cytoplasm and membrane. In primary lung tumors, 54 out of 101 samples exhibited high expression of CFH and high expression was significantly correlated with lung adenocarcinoma (p=0.009). Also, in adenocarcinoma of the lung, Kaplan-Meier survival analysis showed a tendency that CFH-positive tumors had worse prognosis in comparison to CFH-negative tumors (p=0.082). Additionally, shorter survival time of patients with adenocarcinoma (<20 months) was associated with higher staining of CFH (p=0.033). Our data showed that non-small cell lung cancer cells expressed and secreted CFH. CFH might be a novel diagnostic marker for human lung adenocarcinoma.

Complement forms the first defense line of innate immunity and has an important role in the non-inflammatory clearance of apoptotic and necrotic cells. Factor H is one essential complement inhibitor that binds to the acute phase reactant C-reactive protein (CRP). By using recombinant proteins, calcium-independent binding of Factor H to monomeric CRP (mCRP), but not to pentameric CRP (pCRP), was shown. In addition to the two known CRP-binding sites, a novel third site was localized within the C-terminus. This region is frequently mutated in the hemolytic uremic syndrome and the mutant proteins show reduced mCRP binding. In this study, we show that mCRP directs Factor H to the surface of apoptotic and necrotic endothelial cells and identify phosphocholine as one binding moiety for this complex. Factor H-mCRP complexes enhance C3b inactivation both in the fluid phase and on the surface of damaged cells and inhibit the production of pro-inflammatory cytokines. By recruiting the soluble complement inhibitor Factor H to the surface of damaged cells, mCRP blocks the progression of the complement cascade beyond the step of the C3 convertase, prevents the formation of inflammatory activation products, and thus contributes to the safe removal of opsonized damaged cells and particles.