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14 Cards in this Set
- Front
- Back
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Compare BCR & TCR
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BCR:
-2 H and 2 L -Has membrane (IgM) & secreted form (IgG) -Undergoes class switching -Undergoes affinity maturation TCR: -1 alpha and 1 beta chain -Exists only in membrane form -Does not undergo class switching or affinity maturation (carries one antigen specificty for life) |
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VDJ Recombination
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Occurs for B/T cell development
Generates diversity Mediated by enzyme recombinase RAG-1 and RAG-2 at the somatic level. |
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Function of Recominase enzyme
How does it work? |
Recognize DNA regions between V, D, and J gene segments and brings them closer together.
Exonucleases cut DNA at the ends and breaks are repaired by ligases Can chose different V, D, and J segments which leads to diversity. This process is irreversible |
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What are the steps for VDJ recombination of a B cell?
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1. D and J segments become DJ because they are close to each other.
2. DJ then links with V segment 3. Splicing then ligates VDJ with C(micro) 4. VDJC(micro) combines with surrogate L chain to become pre-B cell. 5. V segment ligates to J segment on L chain locus 6. Complete IgM and IgD expresses on B cell surface to become mature B cell. |
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The number of H, V, D, and J's multiplied together.
Limited by the number of available V, D, and J segments |
combinatorial diversity
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Nucleotides are removed by exonuclease (creates more diversity).
Terminal Deoxyribonucleotidyl Transferase (TdT) adds nucleotides to the N-region |
Junctional diversity
Unlike combinatorial diversity, junctional diversity is unlimited |
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What are the mechanisms for generating diversity?
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1. Combinatorial diversity
2. Junctional diversity 3. Affinity maturation (only in B cells)-after antigen stimulation, somatic mutation & selection increase antibody affinity) |
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What stimulates proliferation of BOTH B and T lymphocytes?
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IL-7
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Where do thymocytes receive "education"?
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Cortex
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Where do thymocytes gather the T cells after positve and negative selection?
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Medulla
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What are the stages of T cell development?
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1. Double negative stage
2. Pre T(alpha) 3. Double positive stage |
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Double negative stage
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No CD8 and no CD4
Same as pro-B |
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Double positive stage
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CD8 and CD4 both present on surface. They get tested by dendritic cells to see:
1. If they recognize MHC II with CD4 2. If they recognize MHC I with CD8 |
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Negative selection
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Clonal deletion of self
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