C5a is a small protein fragment 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. C5a is generated when the protein C5 is cleaved, and it acts as a powerful chemotactic factor, attracting immune cells to sites of inflammation. Once released, C5a binds to specific receptors on immune cells, enhancing their ability to respond to pathogens. This process can lead to increased inflammation, which is essential for fighting infections but can also contribute to tissue damage if not regulated properly.