Glycoprotein that plays an essential role in maintaining a well-balanced immune response by modulating complement activation. Acts as a soluble inhibitor of complement, where its binding to self markers such as glycan structures prevents complement activation and amplification on cell surfaces (PubMed:21285368, PubMed:25402769). Accelerates the decay of the complement alternative pathway (AP) C3 convertase C3bBb, thus preventing local formation of more C3b, the central player of the complement amplification loop (PubMed:19503104, PubMed:26700768). As a cofactor of the serine protease factor I, CFH also regulates proteolytic degradation of already-deposited C3b (PubMed:18252712, PubMed:28671664). In addition, mediates several cellular responses through interaction with specific receptors. For example, interacts with CR3/ITGAM receptor and thereby mediates the adhesion of human neutrophils to different pathogens. In turn, these pathogens are phagocytosed and destroyed (PubMed:9558116, PubMed:20008295). Homodimer (PubMed:18005991, PubMed:19505476). Forms also homooligomers (PubMed:19505476). Interacts with complement protein C3b; this interaction inhibits complement activation (PubMed:16601698, PubMed:19503104, PubMed:20378178, PubMed:21285368, PubMed:28671664). Interacts with complement protein C3d (PubMed:20378178, PubMed:21285368, PubMed:29190743). Interacts with CR3/ITGAM; this interaction mediates adhesion of neutrophils to pathogens leading to pathogen clearance (PubMed:9558116, PubMed:20008295). Interacts with complement factor I (PubMed:28671664). (Microbial infection) Interacts with West nile virus non-structural protein 1 (NS1); this interaction leads to the degradation of C3. (Microbial infection) Interacts with C.albicans GPD2; the interaction is direct and leads to the degradation of C3 which enables the pathogen to evade the host innate immune system. (Microbial infection) Interacts with Neisseria meningitidis protein fHbp. (Microbial infection) Interacts with Borrelia burgdorferi outer surface protein E/OspE; this interaction recruits complement regulator factor H onto the bacterial surface to evade complement-mediated cell lysis. (Microbial infection) Interacts with Streptococcus pneumoniae protein virulence factor choline-binding protein A/CbpAN; this interaction enables Streptococcus pneumoniae to evade surveillance by human complement system. (Microbial infection) Interacts with Staphylococcus aureus surface protein serine-aspartate repeat protein E/SdrE; this interaction sequesters CFH on the surface of S. aureus for complement evasion. (Microbial infection) Interacts with Staphylococcus aureus protein Sbi; this interaction inhibits the complement activation of the alternative pathway. (Microbial infection) Interacts (via sushi 4-6 domains) with P.falciparum surface protein PF92; the interaction recruits CFH onto the merozoite surface preventing complement-mediated cell lysis (PubMed:26700768). The interaction does not affect CFH activity (PubMed:26700768). (Microbial infection) Interacts (via sushi 4-6 domains) with P.falciparum surface protein PF92; the interaction recruits FHL-1 isoform onto the merozoite surface preventing complement-mediated cell lysis (PubMed:26700768). The interaction does not affect FHL-1 isoform activity (PubMed:26700768). Expressed in the retinal pigment epithelium (at protein level) (PubMed:25136834). CFH is one of the most abundant complement components in blood where the liver is the major source of CFH protein in vivo. in addition, CFH is secreted by additional cell types including monocytes, fibroblasts, or endothelial cells (PubMed:6444659, PubMed:2968404, PubMed:2139673, PubMed:25136834). Sushi 1-3 domain represents the minimal unit capable of cofactor activity (PubMed:18252712). The property to discriminate self surfaces from non-self surfaces depends on the C-terminal region made of Sushis 19-20 (PubMed:21285368). Sulfated on tyrosine residues. The gene represented in this entry is involved in disease pathogenesis. The disease is caused by variants affecting the gene represented in this entry. Disease susceptibility is associated with variants affecting the gene represented in this entry. Other genes may play a role in modifying the phenotype. Disease susceptibility is associated with variants affecting the gene represented in this entry. According to a report, Asn-217 is not glycosylated (PubMed:17591618). Another study observed glycosylation at this position (PubMed:19139490). CFH mutation db