module 08 section 03 (lectin pathway)

Question 1

how does the lectin pathway begin?

Answer 1

mannose-binding lectin binds mannose, glucose or other sugars in terminal positions on carbohydrate or glycoprotein components of microorganisms

Question 2

mannose-binding lectin belongs to which protein family?

Answer 2

collectin family

Question 3

where is the collectin family produced?

Answer 3

liver

Question 4

how can mannose-binding lectin initiate the complement cascade?

Answer 4

by binding to pathogen surfaces

Question 5

what is step 1 of the lectin pathway?

Answer 5

• serum mannose-binding lectin binds to mannose residues on glycoproteins or carbohydrates on surface of microbes
• mannose-binding lectin is an acute phase protein produced during inflammation

Question 6

recall: mannose-binding lectin is a structural analogue of what protein?

Answer 6

C1q

Question 7

what is step 2 of the lectin pathway?

Answer 7

mannose-binding lectin-associated serine protease (MASP) binds to mannose-binding lectin (MBL)

Question 8

what is step 3 of the lectin pathway?

Answer 8

the active MASP-MBL complex cleaves inactive C4 into active C4a and C4b

Question 9

what is step 4 of the lectin pathway?

Answer 9

• C4b can covalently attach to the pathogen cell membrane via mannose binding
• after that, C2 binds C4b

Question 10

what is step 5 of the lectin pathway?

Answer 10

-C2 of the C4bC2 complex is cleaved by MASP to form C4bC2a - which is C3 convertase

Question 11

what is important to note about the lectin pathway after step 5?

Answer 11

same as the classical pathway

Question 12

what is step 6 of the lectin pathway?

Answer 12

C3 convertase binds to and cleaves C3 into C3b and C3a

Question 13

what is step 7 of the lectin pathway?

Answer 13

• C3b molecules bind to C4bC2a to form C5 convertase
• unbound C3b can either be hydrolized (where it becomes inactive) or It can form covalent bonds with target cell surfaces

Question 14

what is step 8 of the lectin pathway?

Answer 14

• C5 convertase binds to C5 and cleaves it into C5b

- recall - this is the end protein that all three complement pathways create

Question 15

Question: the classical and lectin complement pathway cascades meet at the complement protein:

Answer 15

C4bC2a