The complement System

Question 1

What is the definition of inflammation?

Answer 1

The process of vascularized tissues, with fluid and leukocytes accumulation at the site of injury.

Question 2

Transudation

Answer 2

The movement of fluid with low levels of plasma protein.

Question 3

Exudation

Answer 3

The movement of leukocytes and high levels of plasma protein.

Question 4

Fibrinous Exudate

Answer 4

Large amounts of FIBRIN

Question 5

Purulent Exudate

Answer 5

Large amounts of neutrophils

Question 6

Suppurative Inflammation

Answer 6

An inflammation with purulent exudate due to liquefactive necrosis.

Question 7

What are 3 main functions of the complement system?

Answer 7

“OIL”

1. Opsonization
2. Inflammatory (pro-)
3. Lysis (Membrane Attack Complex)

Question 8

Complement Activation Pathways In Order

Answer 8

1. Alternative Pathway
2. Lectin Pathway
3. Classic Pathway

Question 9

Alternative Pathway

Answer 9

• Activated when factor B binds to C3b on the microbial surface.
• Its C3bBb (C3 convertase) converts C3 to C3a and C3b.
• Its C3bBb bind to C3b and forms C3bBb3b (C5 convertase).
• Its C3bBb3b converts C5 to C5a and C5b.
• C5b forms MAC along with C6-C9.

Question 10

Lectin Pathway

Answer 10

• Activated when “mannose binding lectin (MBL)” binds to mannose sugar on microbial surfaces.
• Its C4b2b (C3 convertase) converts C3 to C3a and C3b.
• Its C4b2b bind to C3b and forms C4b2b3b (C5 convertase).
• Its C4b2b3b converts C5 to C5a and C5b.
• C5b forms MAC along with C6-C9.

Question 11

Classic Pathway

Answer 11

• Activated when Fc portion of an antibody binds with C1q.
• Its C4b2b (C3 convertase) converts C3 to C3a and C3b.
• Its C4b2b bind to C3b and forms C4b2b3b (C5 convertase).
• Its C4b2b3b converts C5 to C5a and C5b.
• C5b forms MAC along with C6-C9.

Question 12

What complement protein functions as an opsonin?

Answer 12

C3b

Question 13

What complement proteins function as anaphylatoxins?

Answer 13

C3a, C4a, and C5a

Question 14

What complement proteins form MAC to lyse the microbe?

Answer 14

C5b and C6-C9

Question 15

What is the function of DAF?

Answer 15

Decay-Accelerating Factor down-regulates the C3 convertase by displacing Bb from C3bBb.

Question 16

What happens with DAF deficiency?

Answer 16

The complement activation will be uncontrolled leading to RBC lysis, causing PNH (Paroxysmal Nocturnal Hemoglobinuria).

Question 17

What is the function of C1-INH?

Answer 17

C1-Inhibitor is a protease inhibitor that down-regulates C1r and C12 activation in the classical pathway.

• C1-INH down-regulates the Bradykinin Pathway.

Question 18

What happens with C1-INH Deficiency?

Answer 18

C1 activation will be uncontrolled leading to excessive vasoactive peptides being generated, causing Hereditary Angioedema.

Question 19

What happens with C3 deficiency?

Answer 19

Results in recurrent pyogenic (causing pus) infections and profound risk of encapsulated bacteria infection.

Question 20

What happens with C5b, C6, C7, C8, and C9 deficiency?

Answer 20

Increased susceptibility to Neisseria Infections.

Question 21

What happens with C1, C2, C4 deficiency?

Answer 21

Increased risk of immune complex disease, SLE.

Question 22

What happens with C1-INH deficiency?

Answer 22

Excess of vasoactive peptides (bradykinin generated), causing Hereditary Angioedema.