Immunology - 6 - B cells

Question 1

Compare and contrast the B lymphocyte and T lymphocyte receptors for antigen.

Answer 1

• B cells - recognize epitopes
• T cell - recoginze only SMALL peptides

Question 2

Describe the structures of the various isotypes of antibodies

Answer 2

Isotype Abs:

B-cell

• IgM
  
  • complement activation (classical pathway)
  • 1st to be produced

Helper T cells: CD40L + Cytokines

• IgG (IFN-y)
  
  • Fc receptor-dependent phagocyte responses
  • complement activation (classical pathway)
  • neonatal immunity (placental transfer)
    
    • neutralization of microbes + toxins
    • opsonization of Ag for phagocytosis
    • feedback inhibition of B cell activation
• IgE (IL-4)
  
  • Immunity against helminths
  • induce fEEEver
  • Mast cell degranulation
    
    • immediate hypersensitivy response
• IgA (TGF-beta; BAFF)
  
  • Mucosal + respiratory immunity
  • neuralization of microbes & toxins

Question 3

Describe the process of B cell development and maturation.

Answer 3

B Cell Maturation: (Bone Marrow)

• Stem cell
• Pro-B
• Pre-B (Pre-BCR)
  
  • recombined H chain gene (VDJ)
• Immature B (IgM)
  
  • recombined H chain gene
• Mature B (IgM + IgD)
  
  • alternative splicing of primary transcript to

Question 4

Outline VDJ rearrangement for class switching of antibodies.

Question 5

process of B cell activation.

Answer 5

Humoral Response

• Ag recognition
  
  • by naive IgM+, IgD+ B cell + microbe
• Activated B cell
  
  • Activation of B lymphocytes
• Clonal expansion
  
  • —> Differentiation
    
    • 1. Effector cells = Ab secreting plasma cells
         * Ab secretion
    • 2. IgG expressing B cells
         * Isotype switching
    • 3. High Affinity Ig-expressing B cell
         * affinity maturation = high affinity IgG
         * memory B cell

Question 6

Compare and contrast follicular, marginal zone, and B1-B B lymphocytes.

Answer 6

3 B Cell - Subsets:

1. Follicular B cells
   
   1. protein Ag + helper T cells
   2. Germinal center rxn in lymph node/spleen
   3. Isotype-switched; high affinity Abs; long-lived plasma cells
      
      1. IgG, IgA, IgE
2. Marginal zone B cells
   
   1. polysaccharides, lipids, etc
   2. Spleen/lymphoid organ
   3. Maingly IgM; short-lived plasma cells
3. B-1 B cells
   
   1. polysaccharides, lipids, etc,
   2. IgM + CD5 –> mucosal tissue/peritoneal cavity
   3. Mainly IgM; short-lived plasma cells

Question 7

Outline the primary and secondary antibody responses.

Answer 7

Primary response:

• 1st infection (0-30 days)
  
  • naive B cell
  • activated B cells
  • plasma cells in peripherallymphoid tissues
    
    • IgG + IgM (low affinity) ~ day 10
  • Plasma cells in bone marrow
    
    • low-level anti-body production

Secondary response:

• Repeat infection (0 - 30 days)
  
  • memory B cell
  • plasma cells
    
    • IgG (high affinity) ~ day 5
  • plasma cells in bone marrow
    
    • produce more Ab
  • memory B cell level = higher than before
• **FASTER, BETTER based on memory

Question 8

Delineate the process of B cell presenting antigen to helper T lymphocytes.

Answer 8

1. B-cell activation in follicle
   
   • moves to extrafollicular space (T-cell zone)
     
     • initial T-B-interation
2. Dendritic cell presents Ag to helper T cell
   
   • T cell activation of effector T cells
     
     • Initial T-B-interaction
3. T-B-interation lead to…
   
   • short-lived plasma cells
     
     • extrafollicular helper T cell
4. Germinal Center Rxn
   
   • folliciular dendritic cell + follicular helpet T cell
     
     • allowing for isotype switching & long lived plasma cells

___________

• B cell Ag presentation to activate helper T cells
  
  • T cell :: TCR :: Peptide :: MHC II :: B cell
  • CD40L :: CD40 on B cell
  • cytokine :: cytokine receptor on B cell
• ​Activation of B cells by CD40 ligand + cytokines –>
  
  • B cell proliferation; initial Ab production, germinal center rxn

Question 9

Describe the effector functions of B lymphocytes.

Answer 9

• B cell + microbe –> Abs
  
  • Phagocyte –>
    
    • neutralization of microbe/toxin
    • opsonization + phagocytosis of microbe
      
      • w/ Fc receptor
  • NK cell –>
    
    • Ab-dependent cellular cytotoxicity
      
      • w/ Fc receptor
  • Complement activation
    
    • C3b recepter –>
      
      • phagocytosis of microbes opsonized w/ complement fragments
    • Inflammation
    • Lysis of microbe