lektiinireitillä

Lektiinireitillä is a Finnish term that translates to "on the lectin pathway." This refers to one of the three main activation pathways of the complement system, a critical component of the innate immune system. The lectin pathway is initiated by the binding of certain carbohydrate-binding proteins, known as lectins, to specific sugar molecules found on the surface of pathogens.

The key lectin involved in this pathway is mannose-binding lectin (MBL). When MBL encounters a pathogen displaying mannose or other specific sugars on its surface, it binds to these structures. This binding event triggers a cascade of enzymatic reactions. MBL associates with MBL-associated serine proteases (MASPs), which then cleave complement components C4 and C2. This cleavage generates C3 convertase, an enzyme that amplifies the complement response by cleaving C3.

The consequences of C3 cleavage are similar to those activated by the other complement pathways: opsonization (marking pathogens for phagocytosis), inflammation, and the formation of the membrane attack complex (MAC), which can lyse (burst) target cells. The lectin pathway serves as an important bridge between innate and adaptive immunity, as it can recognize a broad range of microbial carbohydrates without prior exposure. Its activation is crucial for the early defense against invading microorganisms.