Lectin Pathway

Question 1

Does the Lectin pathway involve Ab?

Answer 1

No

Question 2

How is the activation of the lectin apthway mediated?

Answer 2

By the surface of the pathogen

Question 3

What does Lectin use instead of C1q to bind?

Answer 3

Mannose binding Lectin (MBL) or Ficolins

Question 4

What is Lectin?

Answer 4

A protein that binds sugars

Question 5

What do MBL and Ficolins bind to?

Answer 5

Specific carbohydrate residues on the pathogen.

Question 6

What are the C1r and C1s equivalents?

Answer 6

MASP-1 and MASP-2

Question 7

Once MBL or Ficolin bind to the carbohydrate what happens next?

Answer 7

C4 is cleaved

Question 8

C4b binds C2 and then what happens?

Answer 8

C2 is cleaved by MBL or Ficolin - leaving C4bC2a on target surface (C3 convertase)

Question 9

What two things does C3 do?

Answer 9

Cleavage of C3 by MBL or Ficolin, C3b binds target surface (opsonin)
Some C3b binds C4bC2a forming C4bC2aC3b (C5 convertase)

Question 10

Alternate Pathway does not involve any initiator molecules. What happens instead?

Answer 10

A small amount of curculating C3 spont. activate - “tick-over”

Question 11

“Tick-Over”

Answer 11

Spont. activation of C3

Question 12

How is activated C3b inactivated?

Answer 12

hydrolysis (binds water)

Question 13

What can C3b on an activator surface bind?

Answer 13

Factor B

Question 14

What cleaves Factor B?

Answer 14

Factor D

Question 15

What results when Factor D cleaves Factor B?

Answer 15

2 fragments

Ba and Bb

Question 16

What is the alternate pathway C3 convertase?

Answer 16

C3bBb

Question 17

What does the C3 convertase facilitate?

Answer 17

Large scale cleavage of C3 producing more C3b

Question 18

What does the additional C3b do?

Answer 18

Binds to the C3bBb to form C3bBbC3b (C5 convertase)

Question 19

Describe the alternate pathway

Answer 19

1. C3b deposited by classical or lectin pathway
2. C3b finds Factor B
3. Factor D cleaves Factor B into Ba and Bb
4. Ba is released, Bb binds to C3b and makes the C3 convertase C3bBb
5. C3bBb can cleave more C3b and make C3bBbC3b (C5 convertase)

Question 20

What factor stabilizes C3bBb activity?

Answer 20

Factor P

Question 21

What factor prevents C3b from binding Factor B?

Answer 21

Factor H

Question 22

Molecules in classical:

Answer 22

C1-C4b-C2a-C3convertase(C4bC2a)-C3b-C4bC2aC3b (C5convertase)-C5b

Question 23

Molecules in alternate:

Answer 23

C3b-Bb-C3bBb(C3convertase)-C3bBbC3b(C5convertase)-C5b

Question 24

Molecules in Lectin:

Answer 24

MBL/Ficolin-C4b-C2a-C4bC2a(C3convertase)-C3b-C4bC2aC3b(C5convertase)-C5b