Complement Component C4 is a protein that plays a crucial role in the immune system. It is part of the complement system, which helps the body fight infections and clear damaged cells. When activated, C4 can bind to pathogens, marking them for destruction by other immune cells. C4 exists in two forms, C4a and C4b, which are produced during the complement activation process. This activation can occur through different pathways, including the classical and lectin pathways. By facilitating inflammation and enhancing the ability of antibodies to eliminate pathogens, C4 is essential for maintaining a healthy immune response.