Pathway: Alternative complement activation
Reactions in pathway: Alternative complement activation :
Alternative complement activation
The proteins participating in alternative pathway activation are C3 (and C3b), the factors B, D, and properdin. In the first place, alternative pathway activation is a positive feedback mechanism to increase C3b. When C3b binds covalently to sugars on a cell surface, it can become protected. Then Factor B binds to C3b. In the presence of Factor D, bound Factor B is cleaved to Ba and Bb. Bb contains the active site for a C3 convertase. Properdin then binds to C3bBb to stabilize the C3bBb convertase on cell surface leading to cleavage of C3. Finally, a C3bBb3b complex forms and this is a C5 convertase.
Innate immunity encompases the nonspecific part of immunity tha are part of an individual's natural biologic makeup
Humans are exposed to millions of potential pathogens daily, through contact, ingestion, and inhalation. Our ability to avoid infection depends on the adaptive immune system and during the first critical hours and days of exposure to a new pathogen, our innate immune system.