Complements

C3 is activated by classical and alternative pathways.

Classical pathway

C1 (q,r,s), C2, C3, C3 are components

C43b cleaves and activates C3

Activated by Ab-Ag complexes

Alternative pathway

C3, factor D, factor B, properdin are components

C3bBb activates C3

Activated by endotoxin, bacterial cell wall

Membrane Attack Complex

Helps to penetrate cell membranes, leading to lysis

Neisseria infection leading to meningococcal meningitis often occurs in patients with complement deficiencies of C5-9.

Complements C5, C6, C7, C8, C9 form the Membrane Atttack Complex. C3a - mediates inflammation

C3b - cleaves C5, opsonises, activates alternative pathway

C5a – chemotaxin, mediates inflammation

Cell Adhesion Molecules are important regulatory molecules in inflammation and cell signalling/migration. ICAM-1 which is widely expressed is also implicated in ulcerative colitis and Crohn's