Complement factors are proteins found in the blood that play a crucial role in the immune system. They help the body identify and eliminate pathogens, such as bacteria and viruses, by marking them for destruction. This process is part of the complement system, which enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells. There are several types of complement factors, each designated by a number, such as C1, C2, and so on. These factors work together in a cascade of reactions, leading to the formation of a membrane attack complex that can directly destroy pathogens. Proper functioning of complement factors is essential for maintaining a healthy immune response.