PATHOLOGY

Detailed explanation-1: -The complement system, also known as complement cascade, is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen’s cell membrane.

Detailed explanation-2: -Optimal phagocytosis requires the presence of both antibodies and complement components on the particle. Particles opsonized with IgG or IgM antibodies can activate complement through the classical pathway, resulting in binding of fragments of complement components to the particle.

Detailed explanation-3: -The small fragments C3a, C4a and C5a that are cleaved from serum C3, C4 and C5 during complement activation are called anaphylatoxins (refer to Fig. 3-7). Anaphylatoxins are not just inert by-products: C3a and C5a play important roles in inflammation (C4a is not very active).

Detailed explanation-4: -There are three pathways of complement activation: the classical pathway, which is triggered directly by pathogen or indirectly by antibody binding to the pathogen surface; the MB-lectin pathway; and the alternative pathway, which also provides an amplification loop for the other two pathways.

Detailed explanation-5: -Complement components that are activated in plasma and body fluids are engaged in the regulation of virtually all phases of an acute inflammatory reaction, including changes in vascular flow and caliber, the increase in vascular permeability, extravasation of leukocytes, and chemotaxis.