MASP3

MASP-3, or mannan-binding lectin-associated serine protease 3, is a serine protease that is part of the lectin pathway of the complement system. It is produced by the liver and circulates in the blood as an inactive zymogen. Along with MASP-1 and MASP-2, MASP-3 associates with pattern recognition molecules such as mannose-binding lectin (MBL) and ficolins to form complexes that detect carbohydrate motifs on pathogens.

In the complement cascade, MASP-3 is one of several MASP family members that participate in lectin pathway activation. Its presence in MBL/ficolin complexes supports recognition of pathogens and the initiation of downstream proteolytic events leading to opsonization, inflammation, and lysis. However, compared with MASP-2, the precise contribution of MASP-3 to classical lectin pathway activation is less well defined. MASP-3 is generally considered to be a circulating protease that can be activated in the same milieu as MASP-2, but its substrate specificity and exact role in normal physiology are still being investigated.

Functions attributed to MASP-3 are the subject of ongoing research. Some studies suggest MASP-3 may influence complement activation by modulating the availability or activity of other MASPs, while other work has proposed a potential role in activating components such as pro-factor D and linking to the alternative pathway; results have not been entirely consistent across systems.

Clinical relevance remains exploratory. Variations in MASP-3 levels or activity have been examined for possible associations with infectious or autoimmune conditions, but robust, replicated links are not yet established.

See also: Complement system; Mannose-binding lectin; Ficolin; Pattern recognition receptors.