Factor H

Factor H is one of the proteins in the complement system of the immune system. It assists with the protection of the host tissue from an immune system reaction by binding with the cells of the host, marking them as safe, but it does not bond with pathogens like bacteria or viruses.
Too much factor H in the bloodstream will inhibit the action of the immune system by interfering with its identification of pathogens. Too little will often result in the immune system attacking the healthy cells of the host. 
Several diseases appear to be associated with abnormal levels of factor H, such as schizophrenia, stroke, hemolytic uremic syndrome and macular degeneration.
Factor H at WikipediaCategory:Biology