Final answer:
DAF (Decay Accelerating Factor) protects human cells by accelerating the breakdown of C3 and C5 convertases in the complement cascade, thereby preventing the formation of the MAC and avoiding damage to human cells.
Step-by-step explanation:
Decay Accelerating Factor (DAF) is a critical regulator of the complement pathway on human cells. The complement system is a part of the immune system that enhances the capacity of antibodies and phagocytic cells to clear pathogens from an organism. It is activated through the classical or alternative pathway leading to the formation of a membrane-attack complex (MAC) that can lyse invading pathogens. DAF prevents the formation of the complement complex on the surface of human cells by accelerating the decay of C3 and C5 convertases, enzymes vital in the complement cascade.
The presence of DAF on human cells prevents the binding and formation of C3 and C5 convertases, thereby stopping the sequential activation of the complement system. Without these convertases, the rest of the cascade including the formation of MAC is prevented, protecting human cells from accidental self-attack that could lead to tissue damage. Endogenous regulatory proteins like DAF are essential for distinguishing self from non-self cells, allowing the immune system to target only foreign pathogens without harming the body's own cells.