Complement System

· complement fixation & activation is the chief antibody ammunition used against cellular antigens such as bacteria or mismatched red blood cells

· a system of 9 different enzyme precursors (C-1 - C-9) + several other substances

· found normally in plasma & other body fluids

· enzymes are normally inactive

· when Ab combines with An -> uncover a reactive site on constant portion of Ab -> set in motion a cascade of sequential reactions in the complement system

· see a progressive amplification in the quantities of enzymes produced

· the activated enzymes then attack the invading agent in several different ways & initiate local tissue reactions that provide further protection:

i) Lysis; via proteolytic enzymes of complement

ii) Opsonization & phagocytosis; complement enzymes increase the attraction of phagocytes for the An agent

iii) Chemotaxis; attraction of neutrophiles & phagocytes

iv) Agglutination; complement enzymes change surface of An agent -> increase stickiness

v) Neutralisation of viruses

vi) Inflammatory effects; hyperenia, coagulation, thereby preventing futher movement of agent through tissues