Complement Flashcards Preview

Foundations Test 4 > Complement > Flashcards

Flashcards in Complement Deck (21):

3 complement pathways in short

Lectin - MBL and ficolins recognize and bind carbs on pathogen surface

Classical - C1q interacts with pathogen surface or antibodies bound to surface

Alternative pathway - C3 undergoes spontaenous hydrolysis to C3(H2O) to initiate eventual deposition of C3 convertase on microbial surfaces


All pathways

Generate a C3 convertase which cleaves C3...leaving C3b bound to membrane and releasing C3a


3 consquences of comlement

c3a and c5a recruit phagocytic cells to site of infeciton and promote inflammation

Phagocytes with receptors for C3b engulf and destroy pathogen (opsonization)

Completion of cascade leads to membrane-attack complex


Lectin pathway

MASP-2 associated with MBL (or ficolin) cleaves C4 to C4a and C4b, C4b binds to microbial surface...C4b then binds C2, which is cleaved by MASP-2 to C2a and C2b...C2a forms C4b2a complex and C2b released...C4b2a is a C3 convertase that cleaves C3 into C3a and C3b...c3b bind to microbial surface and complex with C4b2a3b to make a C5 convertase


Classical pathway

C1q associated with serine proteases C1r and C1s binds antibody...C1r and C1s cleave C4 and then same as lectin


Alternative pathway

Amplification of other pathways

C3b deposied by classical or lectin pathway...C3b binds factor B...Factor B cleaved by factor D into Ba and Bb...C3bBb complex is a C3 convertase that cleaves more C3 molecules into C3a and C3b



C3 undergoes spontaneous hydrolysis to form C3(H2O) which binds factor B...allows it to be cleaved by factor D into Ba and Bb...C3(H2O)Bb complex is a c3 convertase...C3b rapidly inactivated unless near cell surface...Factor B binds C3b on cell surface and cleaved to Bb by factor D


What do pathogens lack and what is present to help?

Properdin (factor) P because lack complement-regulatory proteins...binds C3 convertase and pathogen surface to stabilize


C5 convertase formation

C3b binds C4b2a or C3bBb to form C4b2a3b or C3b2Bb...C5 binds to C3b component of the enzyme...C5 is cleaved by C2a or Bb to form C5a or C5b...C5b remains bound



C5b binds C6 and C7...C5b67 complexes with membrane via C7...C8 binds and inserts into membrane...C9 binds and polymerize...10-16 molecules of C9 form pore into membrane


Regulation of C1q/C1r/C1s complex

C1INH dissociates C1r and C1s from active C1 complex (classical)


Regulation of C4b2a (c3 convertase)

DAF, C4BP, and CR1 displace C2a from complex....C4b bound by C4BP, MCP, or CR1 is cleaved by protease I into C4d and C4c


Regulation of C5 convertase

CR1 and H displace C3b. CR1 and H act as cofactors in cleave of C3b by I


Regulation of MAC

CD59 prevents final assembly of C9 onto the complex


Low C3 levels

Lead to increased numbers of bacterial infection


What leads to hemolytic anemia and how

uncontrolled MAC formation...could be absense of CD59 that inhibits MAC formation


C3b does NOT

Increase vascular permeability


C2b is important in which system



MAC complex deficiency

Neisseria recurrent infection


Cleave products of ____ pathway interact with kinin system

Classical pathway


Factor I deficiency

Leads to recurrent bacterial infections...Factor B would be undetectable