Complemet deficiencies Flashcards
How is the classical pathway activated?
C1q binds to antibody complexes, recruits C1r and C1s.
Clevage of C4 and C2.
Forms C3 convertase C4b2b
Release anaphylatoxins C4a C2a.
How is mannose binding lectin pathway actiavted?
MBL binds mannose sugars, MASP1 and MASP2 bind.
Triggers C4 and C2 cleavage.
Forms C3 convertase C4b2b
Releases anaphylatoxins C4a C2a.
How is alternative pathway activated?
C3 spontaneously cleaved in serum to C3b which binds the surface.
Factor B binds surface C3b. Factor D than claves factor B bound.
Forms C3 convertase C3bBb.
Releases C3a.
What is the classical and alternative C5 convertase?
C4b2b3b
C3bBb3b
Which proteins form the MAC?
C5b, 6, 7, 8, 9.
Three most important mediators of inflammation?
C5a, C4a and C3a.
What are the 5 complement receptors?
CR1, CR2 (CD21), CR3 (CD11b CD18) and CR4 (CD11c CD18).
And C1qR.
What is LFA-1 a heterodimer of?
CD11a/ CD18.
What do C1 inhibitor and C4-binding protein (C4BP) do?
C1INH can bind C1r and C1s to prevent them binding C1q.
C4BP binds C4b to displace C2b.
how does CR1 inhibit the classical and alternative pathway.
How does Factor H inhibit the alternative pathway?
CR1 will bind C4b to displace C2b.
Or C3b to displace Bb.
Factor H will bind C3b to displace Bb.
How does DAF and CD59 inhibit complement activation?
DAF desplaces Bb from C3b.
Or displaces C2b from C4b.
CD59 will inhibit the formation of MAC.
What cells express CR1?
phagocytes, erythrocytes and lympocytes.
What cells express CR2 (CD21)?
B cells and follicular DCs.
What cells express CR3 and CR4?
monoculear phagocytes and NK cells express CD11b/c CD18.
What 5 roles can complement play?
1) Inflammation and chemoattraction.
2) opsonisation
3) Removal of immune complexes
4) lysis through MAC.
5) activation of B cells ( through CR2 (CD21).
What does SPURR stand for?
severe persistent unusual recurrent running in family?
Which of the SPURR did complement case study feature?
severe: N. meningitidis- loss of memory.
unusual: Was with serogroup Y.
recurrent: 3 N. meningitidis infections.
What are pneumococcal infections?
Caused by Strep. pneumoniae.
e.g. otitis media, conjuctivits, sinuisitis.
Pneumonia, empyema, peritonitis, meningitis
What would be first test for complement problems? What can low levels of both tell you?
C3 and C4 levels.
Low levels of both can be indicative of complement activation. e.g. in SLE.
What could low levels of C4 indicate?
C1 inhibitor deficiency (normally inhibits C1r/s biding to C1q. So more C1q activation and C4 cleavage).
Could also be a C4 null mutation
Or cyroglobulinemia.
An unusual cause of C3 deficiency?
Indicate presence of C3 nephritic factor.
This is an autoantibody that stabilises the alternative C3bBb C3 convertase.
Increased C3 cleavage.
Why is high levels of C3/4 not useful?
Because they go up as they are acute phase proteins.
What are possible outcomes for Ch50 and Ah50 experiments?
Both normal.
Low Ah50 alone indicates issue with alternative pathway.
Low CH50 indicates issue with classical pathway.
Low both indicates issue with (common) MAC formation.
What infection are MAC complex deficiencies most associated with?
(meningococcal) Neisseria infections.
