complement system

1. complement system The complement system is an essential component of innate immunity, and patients with deficiencies in C3 are highly susceptible to recurrent, often lethal, bacterial infections. Genetic deficiencies in MAC formation (the terminal product of the classical pathway) increase susceptibility to only a limited number of microbes, notably Neisseria bacteria, which have thin cell walls that make them especially susceptible to the lytic action of the MAC. Fifteen or more serum components constitute the complement system, the sequential activation and assembly into functional units of which leads to three main effects: release of peptides active in inflammation (Figure 2, top right); deposition of C3b, a powerful attachment promoter (or ’opsonin’) for phagocytosis, on cell membranes (Figure 2, bottom right); and membrane damage resulting in lysis (Figure 2, bottom left). Together these make it an important part of the defences against microorganisms. Deficiencies of some components can predispose to severe infections, particularly bacterial. http://www.creative-diagnostics.com/complement-system.htm