week 6 - complement

Question 1

classical pathway

Answer 1

triggered when antibodies bind to antigens on a pathogen surface, leading to a cascade and formation of C3 convertase.

Question 2

lectin pathway

Answer 2

triggered when mannose-binding lectin (MBL) binds to specific sugars on the pathogens, starting a cascade similar to the classical pathway.

Question 3

alternative pathway

Answer 3

triggered spontaneously by complement proteins binding directly to microbial surfaces, leading to activation of C3.

Question 4

5 functions of the complement system

Answer 4

1 - opsonization: C3b coats pathogens to make them more recognizable and easier for phagocytes to engulf.
2 - inflammation: complement activation produces anaphylatoxins (C3a and C5a) that trigger inflammation and recruit immune cells to the infection site.
3 - cytolysis: the formation of the membrane attack complex (MAC) punches holes in the pathogen membrane, resulting in cell lysis.
4 - chemotaxis/production of cytokines: complement proteins stimulate the release of cytokines, attracting immune cells (e.g., phagocytes) and causing inflammation.
5 - solubilization of immune complexes: complement helps dissolve immune complexes and clears them from circulation.

Question 5

define complement

Answer 5

complement is a group of proteins in the blood that, when activated, enhance immune responses such as opsonization, inflammation, and pathogen lysis.