Final answer:
d. Factor D ; MASP
The initial protease for the alternative pathway is Factor D, and MASP is the initial protease for the lectin pathway. Factor D activates C3 in the alternative pathway, and MASP initiates the lectin pathway upon binding to pathogen-associated carbohydrates.
Step-by-step explanation:
The initial protease for the alternative pathway is Factor D, whereas MASP is the initial protease for the lectin pathway. In the alternative pathway, Factor D is essential for the proteolytic activation of complement component C3 in the absence of antibodies, making it antibody-independent.
The lectin pathway is similar to the classic pathway but is initiated by mannose-binding lectin (MBL) or ficolins binding to specific carbohydrate patterns on pathogens.
Once these proteins are bound, MASP (MBL-associated serine protease) becomes activated, leading to a cascade of events similar to the classical and alternative pathways, culminating in the formation of the membrane-attack complex that can lyse pathogens.