Osmosis video - Complement system

The complement system is a group of proteins that help the body fight infection. The complement system has three pathways: classical, alternative, and lectin pathways. The classical pathway is activated by antibodies, and the alternative and lectin pathways are activated by molecules called pathogen-associated molecular patterns (PAMPs).

The complement system can kill bacteria, viruses, or other cells damaged or invaded by pathogens. They also promote inflammation, which helps activate the immune system even further, and clear away pathogens and debris.