Komplementveier

Komplementveier refers to a cascade of plasma proteins that are part of the innate immune system. This system acts as a defense mechanism against pathogens and plays a role in inflammation and cellular lysis. The complement system can be activated through three distinct pathways: the classical pathway, the lectin pathway, and the alternative pathway.

The classical pathway is typically initiated by the binding of antibodies to an antigen on the surface of a pathogen. This binding event triggers a series of enzymatic reactions involving complement proteins C1, C4, and C2. The lectin pathway is activated when mannose-binding lectin (MBL) or other pattern recognition molecules bind to specific carbohydrate structures on the surface of microorganisms. This interaction leads to the activation of MBL-associated serine proteases, which then cleave C4 and C2. The alternative pathway is a spontaneous, low-level activation that is amplified in the presence of certain molecules on microbial surfaces, such as the C3 protein.

Regardless of the activation pathway, the ultimate goal is the formation of the C3 convertase enzyme. This enzyme cleaves the C3 protein into two fragments, C3a and C3b. C3b can opsonize pathogens, marking them for phagocytosis by immune cells. C3a acts as an anaphylatoxin, promoting inflammation by recruiting immune cells to the site of infection. Further downstream, the formation of the membrane attack complex (MAC) from C5, C6, C7, C8, and C9 leads to the lysis of pathogens by creating pores in their cell membranes. The complement system is tightly regulated to prevent damage to host cells.