Question

What are the consequences of a mutation in the C3 protein that impairs the functioning of C3a, but has no effect on C3b (select all that apply)?

a. Reduced binding of Mannose Binding Lectin or Ficolin to the pathogen

b. Impaired recruitment of macrophages to site of infection

c. Impaired formation of Membrane Attack Complex

d. Impaired binding of Complement Receptor 1 (CR1) to the pathogen

e. Reduced levels of histamines and other inflammatory mediators at site of infection

Answer 1

The correct answer is-

e. Reduced levels of histamines and other inflammatory mediators at site of infection

C3-convertase which is also known as C4b2a catalyzes the proteolytic cleavage of C3 into C3a and C3b, which are generated during activation through the classical pathway and the lectin pathway. C3a is an anaphylotoxin and the precursor of some cytokines such as ASP while C3b serves as an opsonizing agent.

The C3a is an anaphylotoxin which cause smooth muscle contraction, vasodilation, histamine release from mast cells, and enhanced vascular permeability. They also mediate chemotaxis, inflammation, and generation of cytotoxic oxygen radicals