Complement pathway Flashcards
Classical pathway?
An antibody binds to an antigen. C1 complex binds C3 convertase makes C3a and C3b C5 convertase makes C5a and C5b C5b + C6-C9 = MAC complex = lyses cells
Alternative pathway
C3b binds a microbe, creating C4b and 2a
C3 convertase makes C3a and C3b
C5 convertase makes C5a and C5b
C5b + C6-C9 = MAC complex = lyses cells
Mannose binding lectin pathway
Mannose binding lectin binds lectin, creating C4b and 2a
C3 convertase makes C3a and C3b
C5 convertase makes C5a and C5b
C5b + C6-C9 = MAC complex = lyses cells
Role of C3a
Recruitment and activation of leukocytes
Role of C4a
Recruitment and activation of leukocytes
Role of C5a
Potent recruitor of PMNs
Role of C3b
1) Major opsonin along with IgG
2) Causes cascade that leads to MAC
3) Causes cascade that leads to C3a, C4a, and C5a
What activates alternative pathway?
Spontaneous and microbial surface (antibody independent)
What activates classical pathway?
An antibody bound to an antigen (antibody-antigen complexes)
What activates the mannose binding lectin pathway?
Mannose, bound by lectins.
C1 esterase inhibitor deficiency
Hereditary angioedema (don’t give ACE inhibitors)
C3 deficiency
1) Pyogenic URI
2) Increased susceptibility to Type III HS (no C3 === Type III)
C5-C9 deficiencies
Increased susceptibility to Neisseria
No DAF protein
Cannot inhibit C3 esterase so complement overactive.
Causes PNH and hemolytic anemia.
