komplementtireaktioon

Komplementtireaktio refers to the complement system, a crucial part of the innate immune system. It is a cascade of proteins that are activated when they encounter pathogens or damaged cells. This system plays a vital role in host defense against infections and in the removal of cellular debris.

The complement system consists of over 30 different proteins, many of which are synthesized in the liver. These proteins circulate in the blood in an inactive form. Activation can occur through three main pathways: the classical pathway, the lectin pathway, and the alternative pathway. The classical pathway is typically initiated by antibody binding to an antigen. The lectin pathway is activated by the binding of mannose-binding lectin (MBL) to carbohydrate structures on microbial surfaces. The alternative pathway can be spontaneously activated or triggered by certain microbial surfaces.

Regardless of the initial trigger, all three pathways converge on the cleavage of C3, a central protein in the cascade. This cleavage leads to the formation of C3 fragments, which have diverse functions. Key outcomes of complement activation include opsonization, where complement fragments coat pathogens, making them more easily recognized and phagocytosed by immune cells. Another outcome is direct lysis of pathogens through the formation of the membrane attack complex (MAC), which creates pores in microbial cell membranes. Additionally, complement activation generates anaphylatoxins, small peptides that promote inflammation by recruiting immune cells and increasing vascular permeability.

Dysregulation of the complement system can lead to various diseases, including autoimmune disorders and increased susceptibility to infections. Research into the complement system is ongoing, aiming to develop therapeutic strategies targeting specific components for the treatment of a range of conditions.