IMMUNOLOGY

Detailed explanation-1: -A number of complement proteins are proteases that are themselves activated by proteolytic cleavage. Such enzymes are called zymogens and were first found in the gut.

Detailed explanation-2: -The complement activation products C1q, C3a, C4b, and C3b are recognized by specific receptors on cell surfaces that control cell functions (Table 3).

Detailed explanation-3: -About 50 proteins and protein fragments make up the complement system, including serum proteins, and cell membrane receptors. They account for about 10% of the globulin fraction of blood serum.