Question

a-Explain why complement only has the potential to damage healthy tissues when a pathogen is present, but not when a pathogen is not present.

b- What are 2 ways in which healthy cells are protected from damage by complement?

c- Predict the consequences of a deficiency in particular complement components.

d- What are examples of complement components that are anaphlatoxins and what are their effects?

Answer 1

a. classical pathway of the complement activation begins with the formation of soluble antigen-antibody complexes or with the binding of an antibody to an antigen on a suitable target. IgM and IgG can activate the classical pathway. formation of antigen-antibody complexes induces conformational changes in the Fc portion of IgM that expose a binding site for C1, a component of complement.

alternative pathway of complement activation is antibody-independent. it is triggered by almost any foreign substance (LPS from the outer membrane of Gram-negative bacteria, cell walls of some yeasts, etc)

lectin pathway of complement activation is activated by terminal mannose residues of glycoprotein or polysaccharides found on the surface of bacteria. it does not depend on the antibody for activation.

b. healthy host cells escape the complement action due to the presence of either membrane-bound regulators or soluble proteins. preformed complement regulators on host cells ensure that the host cells are not affected by complement-mediated damage.

C3b molecule, a major component of C5 convertase, bound to healthy host cells is rapidly inactivated.