52. Humoral Immunity, B Cell Activation, Affinity Flashcards Preview

Clinical Pathology > 52. Humoral Immunity, B Cell Activation, Affinity > Flashcards

Flashcards in 52. Humoral Immunity, B Cell Activation, Affinity Deck (10)
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1
Q

Antibody functions

A

1) Virus & toxin neutralization ~ Prevents pathogen-host binding
2) Opsonization + ADCP ~ Phagocytosis
3) Complement fixing/MAC formation (CDC) ~ Phagocytosis or lysis
4) Opsonization + ADCC ~ NK-induced apoptosis

2
Q

What are the different classes of antibodies?

A
  • IgG
  • IgD
  • IgA
  • IgE
  • IgM
3
Q

Expand on B cell activation

A
  • Differentiation and clonal expansion of activated B cells
  • Requires 3 signals
    • Antigen binding to BCRs
    • Co-stimulation by activated Th cell specific to same antigen
    • Th cell-derived cytokines

•Signal transduction pathway

4
Q

Signal transduction pathways

A
  • BCR binding > Activation of tyrosine kinase

* Signal transduction pathway for cell proliferation, differentiation and survival

5
Q

Describe the events of clonal expansion

A
  • Body produces many B cells with unique BCRs
  • When there is a pathogen, the B cells that binds the pathogen the closes will be activated and make more clones of itself and these clones will migrate to the germinal centre for affinity maturation
6
Q

What happens in affinity maturation?

A
  • There is a low affinity antibody
  • This undergoes somatic mutations in variable regions - by AID (activation-induced cytidine deaminase)
  • Leads to selection of high-affinity B cells
  • This will migrate to the light zone, where the FDC will present antigens on the surface, B cells with high enough affinity will try to take as much antigens from its surface and present to the Tfh cells
  • The Tfh cells will give the survival signal
  • The reduced affinity B cells will undergo apoptosis in the light zone

•You repeat this several times until the affinity is high enough and then you go to the class switching stage

7
Q

Affinity maturation and class switching in Germinal Centre

A

1) Clonal expansion
2) Somatic hypermutation
3) Repeats until improved affinity (the disadvantageous mutations lead to apoptotic B cell)
4) Selection
5) Class switching - memory B cells and plasma cells
6) Differentiation

8
Q

Heavy chain class switching

A
  • Only affects heavy chain CONSTANT region
  • Different effector functions – deal with different pathogens

• MINOR: Differential splicing (mRNA level)
- IgM and IgD (last lecture)

• MAJOR: DNA recombination

  • IgM to IgG, IgA, IgE
  • IgG to IgA, IgE

•Class switching is mediated by cytokine signalling

9
Q

Class switch recombination (CSR)

A
  • 1) Cytokine signal; 2) Switch regions; 3) AID and DSB repair proteins
  • Recombination between switch regions
  • Switching only proceeds downstream
  • IgM to IgG, IgA, IgE
  • IgG to IgA, IgE
10
Q

What is the difference between membrane and secreted antibody?

A

SECRETED IgG
- Has tail piece

MEMBRANE IgG
- Has membrane anchor made of hydrophobic transmembrane region and cytoplasmic tail

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