The C antigen is a type of protein found on the surface of certain cells in the body, particularly red blood cells. It plays a crucial role in the immune system by helping the body recognize its own cells and distinguish them from foreign invaders. The presence or absence of specific antigens, including the C antigen, can influence blood compatibility during transfusions. In blood typing, the C antigen is part of the Rh blood group system, which includes other antigens like D and E. Understanding the C antigen is important for safe blood transfusions and organ transplants, as mismatches can lead to serious immune reactions.