Which proteins stop the complement pathway on human cells?

The correct answer is based on the roles of Decay-accelerating factor (DAF) and membrane co-factor protein (MCP) in regulating the complement system, which is part of the immune response.

DAF and MCP are both integral membrane proteins found on human cells that play crucial roles in protecting those cells from the potentially damaging effects of the complement system. DAF disrupts the formation of the C3 convertase enzyme complex, which is a key component in complement activation, thus preventing the initiation of the complement cascade. By binding to C3 and C4 components, DAF effectively accelerates the decay of the complement activation complex.

MCP, on the other hand, not only helps to destabilize the C3 convertase but also acts as a cofactor for factor I, an enzyme that cleaves and inactivates C3b and C4b. This further enhances the ability of human cells to protect themselves from complement-mediated lysis, allowing them to regulate the complement pathway and prevent excessive immune damage.

Together, DAF and MCP serve as critical regulators that ensure complement activity is restricted to pathogens and does not harm host tissues. This regulatory mechanism is vital for maintaining self-tolerance and preventing autoimmune responses.

The other options contain