Complement Cascade Regulators

Question 1

Regulatory protein of the classical and lectin pathways.

It prevents the complement cascade from spiraling out of control, which could damage the host’s cells and tissues.

Answer 1

C1-INH (C1 INHIBITOR)

Question 2

Detaches C1r and C1s from C1q (Inhibits the recognition unit of the classical pathway).

Inactivates MASP-2 (Inhibits the recognition unit of the lectin pathway)

Answer 2

C1-INH acts as a serine protease inhibitor

Question 3

this genetic condition, a deficiency dysfunction in C1-INH leads to unchecked complement activation. causing episodes of severe swelling due to the overproduction of vasoactive peptides.

Answer 3

Hereditary angioedema (HAE)

Question 4

Is a serine protease that inactivates complement components
C3b and C4b in the presence of:

• C4BP (C4-binding protein)
• CR1 (complement receptor 1)
• MCP (membrane cofactor protein)
• DAF (Decay-accelerating factor)

Answer 4

Factor I

Question 5

DECAY ACCELERATING FACTOR (DAF)

Answer 5

CD55

Question 6

is capable of dissociating both classical and alternative pathway C3 convertases.

Answer 6

DAF

Question 7

Displaces Bb and C2a from C3b and C4b, respectively
It can bind to both C3b and C4b in a manner similar to CR1.

Answer 7

DECAY ACCELERATING FACTOR (DAF)

Question 8

It does not prevent initial binding of either C2 or Factor B to the cell but can rapidly dissociate both from their binding sites, thus preventing the assembly of an active C3 convertase.

Answer 8

DECAY ACCELERATING FACTOR (DAF)

Question 9

Protects host cells from bystander lysis

Answer 9

DECAY ACCELERATING FACTOR (DAF)

Question 10

• Principal soluble regulator of the alternative pathway

Answer 10

FACTOR H

Question 11

• Mode of action:
1._______ competes with factor B (B) for binding to spontaneously (hydrolytically)
activated C3b.
2. ____dissociates any C3bBb complexes that form on self-cell surfaces.
3. ______is a cofactor with factor | (FI), enabling cleavage of C3b. The resulting C3bi loses enzymatic activity but is still an opsonin.

Answer 11

Factor H (FH)

Factor H

Factor H

Question 12

acts by binding to the fluid-phase C5b-7 complex, preventing it from attaching to nearby cell membranes.

Answer 12

S-PROTEIN (VITRONECTIN)
• S protein

Question 13

• Inhibits C9 polymerization.

Answer 13

S-PROTEIN (VITRONECTIN)
• S protein

Question 14

MEMBRANE INHIBITOR
OF REACTIVE LYSIS (MIRL)
“

Answer 14

Cb59

Question 15

” It targets a later stage of MAC
assembly.

Answer 15

MEMBRANE INHIBITOR
OF REACTIVE LYSIS (MIRL)
“
Cb59

Question 16

When the C5b-8 complex, having escaped S protein regulation, attempts to insert into the host cell membrane, MIRL binds to C8 and prevents the recruitment and polymerization of C9.

This targeted inhibition ensures that even if the MAC assembles partially on a host cell, it cannot complete its lethal attack.

Answer 16

MEMBRANE INHIBITOR
OF REACTIVE LYSIS (MIRL)