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. 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. As a cofactor of the serine protease factor I, CFH also regulates proteolytic degradation of already-deposited C3b. 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. Homodimer. Forms also homooligomers. Interacts with complement protein C3b; this interaction inhibits complement activation. Interacts with complement protein C3d. Interacts with CR3/ITGAM; this interaction mediates adhesion of neutrophils to pathogens leading to pathogen clearance. 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. Sushi 1-3 domain represents the minimal unit capable of cofactor activity. The property to discriminate self surfaces from non-self surfaces depends on the C-terminal region made of Sushis 19-20. Sulfated on tyrosine residues.