Complement System

Question 1

Alternative pathway C3 and C5 convertases are made of

Answer 1

C3 convertase- C3bBb

C5 convertase- C3bBbC3b

Question 2

Lectin pathway steps

Answer 2

MBL binds to bacterial surface, activates MASP-1 and MASP-2.
MASP-2 cleaves C2 and C4 to form classic C3 convertase C2aC4b
The rest is identical to classical

Question 3

C1 inhibitor

Answer 3

Inactivates C1r, C1s, MASP-1/2

Question 4

DAF

Answer 4

Destabilizes C3/C5 convertases of CP and AP

Question 5

Factor H

Answer 5

Binds C3b, accelerates decay of AP C3/C5 convertases

Question 6

Factor I

Answer 6

Degrades C3b/C4b - aided by CR1, MCP, Factor H and C4BP

Question 7

CD59, S-protein (vitronectin) and Clusterin function

Answer 7

Blocks formation of MAC

Question 8

Which proteins inhibit assembly of C3 convertases in classical pathway

Answer 8

DAF, CR1, C4BP

Question 9

Which proteins inhibit assembly of C3 convertases in alternative pathway

Answer 9

DAF, CR1, Factor H

Question 10

Glomerulonephritis

Answer 10

Result of either deposition of immune complexes or Abs directly binding to Ags in kidney
Classical pathway activated, neutrophils attracted, inflammation and ROS follow

Question 11

Hereditary angioedema

Answer 11

Caused by deficiency in C1 inhibitor
HAE patients exhibit evidence of continuous activation of plasma complement
-C1 also inactivates kallikrein, which produces bradykinin. Without C1, there is too much bradykinin, causing edema

Question 12

Paroxysmal nocturnal hemoglobinuria PNH

Answer 12

Deficiency in glycosylphosphoinositol. GPI usually anchors proteins DAF and CD59, which protect RBCs from the action of complement
RBCs are now more susceptible to compliment, causing hemolysis