Question

Factor H, a complement regulatory protein in plasma, binds C3b and:

• A. ( competes with factor B to displace Bb from convertase. )
• B. ( initiates the catabolism of C3b into inactive products. )
• C. ( then binds to C3bBb convertase. )
• D. ( acts as a cofactor for factor I. )

Hint:

Understanding the roles of regulatory factors like Factor H is crucial in the study of the immune system, particularly in the context of immune regulation and the prevention of autoimmune reactions.

Answer 1

The Correct Option is A

Analysis of Each Statement: 
(A) Competes with factor B: Correct. Factor H competes with factor B for binding to C3b, ultimately displacing Bb from the C3 convertase, C3bBb, thus inhibiting the complement cascade. 
(B) Initiates catabolism: Incorrect. While Factor H influences the degradation of C3b by influencing its environment, it does not itself initiate the catabolism of C3b into inactive products. 
(C) Binds to C3bBb convertase: Incorrect. Factor H does not bind to form part of the C3bBb convertase but rather regulates its activity by competing for C3b binding. 
(D) Acts as a cofactor for factor I: Correct. Factor H acts as a cofactor for factor I, which is responsible for the cleavage of C3b into iC3b, further regulating the complement cascade and preventing unnecessary tissue damage. Conclusion:
Thus, statements (A) and (D) correctly describe the functions of Factor H in the regulation of the complement system, highlighting its crucial role in preventing over-activation of the complement pathway and protecting host cells.