Quiz #2

Question 1

How do B cells mature?

Answer 1

HSC>CLP> B cell precursor (Ig-) >immature B cell(IgM+) > mature B cell (IgM+/IgD+)

Question 2

How do B cells go under negative selection?

Answer 2

Any BCR that recognizes self antigen is detected

Avoids self reactive B cells in the circulation

Question 3

Describe the structure of a BCR?

Answer 3

BCR has two heavy chains, two light chains, and the binding sites are composed of Variable regions, and constant regions
Within the variable region is a hypervariable region

Question 4

What are the 2 signals that B cells need for activation? What is the third signal?

Answer 4

1. Antigen recognition: Ag binds to the Vh and the VL of the BCR, cross linking occurs and Clusters of Iga/B form– results in intracellular signalling
   - B cell processes antigen and displays it on MCHII molecules
2. Costimulation: TCR binds to MHCII peptide and CD40L on T cell binds to CD40 on B cell (1+2= proliferation and effector function)
3. T cell cytokines: influence WHICH antibodies are made

Question 5

How does T cell independent B cell activation occur?

Answer 5

• Triggered by highly repetitive antigens and extensive cross-linking of the BCR to get a strong signal, partial activation,
• Leads to some Ab production, no class switching, no memory

Question 6

What is the function of an antibody?

Answer 6

neutralization, opsonization and complement activation, increasing phagocytosis through opsonization and mast cells

Question 7

IgM properties?

Answer 7

can neutralize pathogens, activate complement, opsonize through complement activation, located in blood

Question 8

IgG properties?

Answer 8

can neutralize pathogens, activate complement, opsonize pathogens, located in blood

Question 9

IgA properties?

Answer 9

IgA: can neutralize pathogens, located in bodily secretions

Question 10

IgE properties?

Answer 10

can activate mast cells, located in the tissues

Question 11

What is neutralization?

Answer 11

Neutralization: antibodies bind the pathogen/toxin and block their interaction with the host
Pathogens and toxins have to bind the host cell to cause disease

Question 12

What is opsonization?

Answer 12

Opsonization: antibodies bind to the pathogen with their variable region, and the constant region binds to the macrophage through the FcR

Question 13

Function of proteins in complement?

Answer 13

C3 breaks down into:
C3a: acts as a chemoattractant to bring out more neutrophils
C3b: sticks to surface of bacterium, leads to formation of C5 convertase
C5a: acts as chemoattractants to bring in more neutrophils
C5b: sticks to surface of the bacterium to trigger MAC formation for lysis

Question 14

Stages of an extracellular bacterial infection? (humoral immunity)

Answer 14

1. Tissue damage is a danger signal to activate mast cell degranulation
   Leads to the characteristic signs of inflammation
2. Macrophages activate by PRR recognition (phagocytic and TLRs) of bac PAMP
   - Alternative activation of complement cascade
   - Macrophages release IL-1, IL-6 and TNFa and CXCL8
3. DC phagocytosis bacteria and migrates to the lymph node to present the peptide to the T cell (could also travel through the lymph node on its own)

Question 15

stages of an Intracellular bacterial infection: (cell-mediated immunity)?

Answer 15

• Have strategies for escaping phagocytosis, like thriving in an acidic environment in the lysosome and then escaping
  1. Resident macrophages produce alarm cytokines (IL-1, Il-6 and TNFa) and DC brings antigen to the lymph nodes to show the T cell, T cell makes IFNy
  2. IFNy from the Th cell goes to the mac and it produces more protons for acidification, nitric oxide, oxygen radicals and hydrogen peroxide, proteases and defensins (hyperactivation of macrophages)
• B cells are less important for an intracellular bacteria because antibodies cant get through the plasma membrane

Question 16

Stages of a viral infection?

Answer 16

1. Both cell- mediated and humoral immunity
   Influenza infects lung cell and hijacks cell to start reproducing virus
   APCs present viral antigen on the MHCI
2. T cell activation: PAMPS (double stranded RNA in example) activate the DC to take up virus by phagocytosis, present through cross presentation and activate both CTL and Th
   CTLs migrate to lung cells and target the infected cells
3. Antibody-mediated neutralization: B cell sees Ag, Th cell provides CD40L and activates B cell, some become memory cells, some become plasma cells to produce antibodies (either IgG or IgA)

Question 17

What are the alarm cytokines?

Answer 17

IL-1
IL-6
TNFa

Question 18

What are the cytokines that the DC releases to affect differentiation of T cells?

Answer 18

IL-12

IL-18

Question 19

Which cytokine affects the proliferation of T cells?

Answer 19

IL-2

Question 20

Which cytokine is a Chemokine for neutrophil recruitment, and related to the alarm cytokine?

Answer 20

IL-8 (CXCL8)