Immunology T5

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  • Created by: Kavita :)
  • Created on: 09-03-15 18:06
Where do B cells derive from?
Hematopoietic stem cell in bone marrow
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What do the early phases of B cell development depend on? Process?
STROMAL CELLS in bone marrow. Interaction of FLT3 (tyrosine kinase receptor) with its ligand is essential to make common lymphoid projenitor. IL-7 produced by stomal cells. Adhesion molecules retain B cell on stromal cell. Allows Kit to bind - divide
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What are large pre-B cells?
Dividing cells which express surrogate light chain and the pre-B cell receptor. These become small pre-B cells and start to rearrange light chain
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What allows surface expression and prevention of further heavy chain gene rearrangements?
The surrogate light chains VpreB & λ5 bind the heavy chain allowing surface expression. Signalling through cross linked receptors lgα + β prevent further heavy chain gene rearrangements
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What is the advantage of repeated rearrangments in the light chains?
Non-productive light chain rearrangements can be rescued
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What are the main phases of immunoglobuline gene rearrangments?
1) Early Pro- Bcell ( H chain D-J) 2) Late Pro-Bcell (H chain V-DJ) 3) Pre- Bcell (L chain κ) 4) Immature B cell (IgM expressed)
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What is the consequence of binding to self molecules?
Cell death or functional anergy
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What mediates the humoral response?
Antibodies secreted by plasma cells - Neutralization Opsonization, Complement Activation
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What are the 2 signals required to activate the humoral response?
1) First signal delivered when immunoglobulin on surface of B cells binds to antigen 2) Second signal delivered by helper T cell recognising degraded fragments of the same antigen (MHC II), interaction between CD40+L release of cytokines
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How is IL-4 released?
Helper T cells adhere to B cells, synthesise IL-4 and CD40L. Helper T cell reorients its cytoskeleton towards B cell. IL-4 is released ad confined to the space between B & T cell.
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How do B cells travel to lymph node and exit?
Travel via blood stream and leave via efferent lymph
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What goes on in the germinal centre?
GC are active sites of B cell proliferation. 10% antigen specific T cells. Unstimulated B cells form a mantle zone of resting B cells on the edge. Affinity maturation, somatic hypermutation and class switching.Differentiate into memory or plasma cell
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Describe the structure of the germinal centre?
Centroblasts undergo somatic hypermutation in the dark zone. They are tested for antigen binding abilotu in the light zone where they contact follicular dendritic cells.
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Which receptors do centrocytes carry?
CXCR5 (not 4) chemokine receptor. Loss and gain of CXCR4 allows the cell to re-enter the dark zone by attraction to CXCL12.
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What sustains the germinal centre?
Interaction with antigen and signalling throigh CD40 pathwat provided by T-FH
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What directs class switching?
Cytokines (IL-4/5, IFN-Y, TGF-B)
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Describe neutralization of harmful bacterial toxins
Antibody protects cell by blocking the binding of the toxin to cell surface - active chain of toxin is poisonous (endocytosis). Virus entry can be blocked - antibodies bind to virus receptor
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Describe complement activation
Clq binding to penameric IgM molecule (staple form) or at least two IgG molecules cleaves and activates serine proteases.
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How do complement receptors remove immune complexes?
Small antigen:antibody complexes form in the circulation. Activation of complement leads to the deposition of many molecules of Cb3 on immune complex. Complement receptor CR1 on RBC binds to immune complexes. Spleen and liver - phagocytotic cells
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What receptors trigger phagocytosis?
Fc + complement receptors on phagocytes.
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What does cross-linking of IgE on surface of mast cells result in?
Degranulation of mast cells + release of inflammatory mediators
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Card 2

Front

What do the early phases of B cell development depend on? Process?

Back

STROMAL CELLS in bone marrow. Interaction of FLT3 (tyrosine kinase receptor) with its ligand is essential to make common lymphoid projenitor. IL-7 produced by stomal cells. Adhesion molecules retain B cell on stromal cell. Allows Kit to bind - divide

Card 3

Front

What are large pre-B cells?

Back

Preview of the front of card 3

Card 4

Front

What allows surface expression and prevention of further heavy chain gene rearrangements?

Back

Preview of the front of card 4

Card 5

Front

What is the advantage of repeated rearrangments in the light chains?

Back

Preview of the front of card 5
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