Question

The
system is a group of proteins in the blood that attack pathogens that enter the body and kill them.

Answer 1

That describes the complement system — a group of plasma proteins (e.g., C3, C5–C9) that help destroy invading microbes. Complement functions include opsonization (coating pathogens to enhance phagocytosis), promoting inflammation, and forming the membrane attack complex (MAC) that lyses target cells. It can be activated via the classical, lectin, or alternative pathways.