Complement

Question 1

Mechanisms following complement activation

Answer 1

1. Opsonisation. Coats surface with C3b proteins to promote phagocytosis.
2. Initiated inflammatory response. Release anaphylatoxins, C3a, C4a and C5a binds to immune cells to trigger the inflammatory response. Anaphylatoxins are also chemist reactants to phagocytes.
3. Punches hole in cell membranes. Formation of the membrane attack complex (MAC) on surface cells, bacteria and envelopes cells.

Question 2

Activation of complement

Answer 2

1. Classical pathway: C1 recognises immune complexes formed by the binding of antibodies (IgG1, IgG3 or IgM) to antigen.
2. Alternative pathway: non-specific activation by bacteria, fungi, parasites and viruses- C3b deposits on surface of microbes.
3. Lectin pathway: mannose binding lectin attaches to mannose sugar residues on bacteria surface.