Which of the following proteins is known to inhibit Factor H and Factor I during C3b deposition?

Factor P, also known as properdin, plays a unique role in the complement system by stabilizing the C3-convertase enzyme complex. Its primary function is to enhance the alternative pathway of complement activation by preventing the degradation of this enzyme complex. This property contributes to the regulation of complement activation.

In contrast to other proteins mentioned, Factor P does not inhibit Factor H and Factor I; rather, it supports the pathway's activation by stabilizing the C3bBb complex, which is important for amplifying the immune response.

MCP (Membrane Co-factor Protein), DAF (Decay Activating Factor), and CR1 (Complement Receptor 1) are all known for their roles in regulating complement activation, particularly through their interaction with C3b and the inhibition of the alternative pathway. These proteins help prevent excessive complement activation and tissue damage. Specifically, MCP promotes the cleavage of C3b by Factor I when bound to C3b, and DAF promotes the decay of the C3 convertase. CR1 also facilitates the inactivation of C3b through its cofactor activity for Factor I.

Understanding the specific interactions and functions of these complement regulatory proteins is critical for grasping the balance in the immune response and the prevention of