Complement factor H (CFH) is a protein (coded by so-called gene) that plays an essential role in maintaining a well-balanced immune response by modulating complement system activation. The complement system is a group of proteins that work together to destroy foreign invaders (such as bacteria and viruses), trigger an inflammatory response, and remove debris from cells and tissues. Complement factor H, together with several related proteins, protects healthy cells by preventing the complement system from being turned on (activated) when it is not needed.