Komplementfragmente

Komplementfragmente are smaller molecules that are generated when the complement system, a part of the innate immune system, is activated. The complement system is a cascade of proteins that helps clear pathogens and damaged cells from the body and promotes inflammation. Activation of this system involves a series of enzymatic cleavages, where larger complement proteins are broken down into smaller active fragments. These fragments play crucial roles in mediating various immune responses.

The primary complement pathways—the classical, lectin, and alternative pathways—all converge at the cleavage of C3. This cleavage produces two major fragments: C3a and C3b. C3a is a small anaphylatoxin that promotes inflammation by binding to receptors on mast cells and basophils, causing the release of histamine and other mediators. C3b is a larger fragment that acts as an opsonin, coating the surface of pathogens or cellular debris to enhance their recognition and phagocytosis by immune cells like macrophages and neutrophils. C3b can also initiate the formation of the C5 convertase, a key enzyme in the terminal cascade.

Further down the cascade, C5 is cleaved into C5a and C5b. C5a is a potent anaphylatoxin and chemoattractant, recruiting immune cells to the site of infection. C5b initiates the formation of the membrane attack complex (MAC), a pore-forming structure that can lyse target cells. Other complement fragments, such as Bb and Da from the alternative pathway, and C2b from the classical pathway, also contribute to the regulation and amplification of the complement cascade, influencing immune cell recruitment and activation. The precise balance and interaction of these fragments are essential for effective host defense.