Effector Mechanisms of Humoral Immunity

Question 0

How does the inhibitory signaling by FCgammaR2B receptor work?

Answer 0

SHIP will block B cell receptor signaling and result in no activation.

Question 1

What are the most efficient opsonins for the phagocytosis of Ags via high affinity FCgammaR1?

Answer 1

IgG1 and IgG3.

Question 2

What three cells work together in the killing of helminths parasites?

Answer 2

IgE, eosinophils, mast cells.

Question 3

What are the functions of C3a and C3b in complement?

Answer 3

C3a- stimulates inflammation.

C3b- binds to surface and functions as an opsonin, leads to formation of MAC.

Question 4

How is the classical pathway initiated?

Answer 4

Binding of C1 to IgM or IgG with bound Ag.

Question 5

How is the lectin pathway of complement activated?

Answer 5

Activation is triggered by the binding of microbial polysaccharides to circulating lectins, such as plasma mannose binding lectin (MBL). MBL will bind to mannose residues on bacteria.

Question 6

The formation of a fully active MAC is accomplished by what molecule?

Answer 6

Binding of C9.

Question 7

What roles do C5a and C5b play in complement?

Answer 7

C5a- inflammation, chemoattractant.

C5b- aids in the formation of the MAC.

Question 8

What are the ligands of the CR1 receptor and what are the overall functions of these ligands binding to this receptor?

Answer 8

Ligands-C3b, C4b.
Functions- Phagocytosis, clearance of immune complexes, promotes dissociation of C3 convertase by acting as a cofactor for cleavage for C3b and C4b. Phagocytes use this receptor to bind and internalize microbes and debris.

Question 9

What are the ligands and functions of the CR2 (CD21) receptor?

Answer 9

Ligands- cleavage products of C3b (C3d, C3dg, iC3b).

Functions- coreceptor for B cell activation, trapping of Ags in GCs, receptor for EBV (epstein-barr virus).

Question 10

What are the ligands and function of the CR3 complement receptor?

Answer 10

Ligands- iC3b, ICAM.

Function- Phagocytosis, leukocyte adhesion to endothelium.

Question 11

What are the ligands and functions of the CR4 receptor?

Answer 11

Ligands- iC3b.

Functions- phagocytosis, cell adhesion.

Question 12

Name complement regulators and their mode of action.

Answer 12

• C1 inhibitor. Functions through a serine protease inhibition.
• Factor I. Functions by cleaving C3b and C4b.
• Factor H. Functions by binding C3b and displaces Bb. Also a cofactor for factor I.
• Membrane cofactor protein (MCP). Functions as cofactor for factor I.
• Decay accelerating factor (DAF)- displaces C2a from C4b and Bb from C3b.

Question 13

What proteins inhibit the formation of the MAC?

Answer 13

CD59 and S protein in the plasma.