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Unformatted text preview: Sheet1 Page 1 Bio360K Test 2 Key 1. If you purify hematopoietic stem cell, how could you assay its function? Please explain the rational of your assay. (5) HSC is capable of self-renewal and differentiation into all the cell lineages in blood. The function can be demonstrated by transferring the HSC into lethally irradiated mice. The irradiation depletes the hematopoietic system of the recipient mice. HSC can restore the hematopoietic system of the recipient mice. Moreover, the rescue is stably maintained given HSC&amp; s capacity of self-renewal. 2. Both B and T cells are derived from common lymphoid progenitors (CLPs). Why do CLPs differentiate into T cells instead of B cells in the thymus? (3) Thymic epithelial cells express delta ligand. This molecule activates the Notch receptor on CLP/DN1 cells and commits the precursor to T cell differentiation. 3. A patient is deficient in the a chain of IL-7 receptor. What would be the consequence of this defect? Why? (3) Without functional IL-7 receptor, B and T cell precursors will not respond to IL-7. The cytokine is critical for the survival and proliferation of early B and T cell progenitors. The deficiency leads to severe reduction in the number of B and T cells. 4. How is a diverse repertoire of antigen binding site generated during B cell maturation? (3) The coding sequences of antigen binding sites are assembled through V(D)J recombination during B cell maturation. Diverse antigen binding sites are formed through the combination of different gene segments. The association of different heavy and light chains adds another layer of complexity. Imprecise joints between gene segments further expand the diversity. Which part of the antigen-binding site is the most diverse? Why? (3) CDR3 of the IgH coincides with the imprecise junctions of both D to J and V to DJ joints. The introduction of N and P-nucleotides into these junctions makes IgH CDR3 the most variable part of the antigen-binding site. 5. Is a single B cell capable of producing antibodies with different antigen binding specificities? Why? (3) Allelic exclusion ensures that each B cell expresses only one kind of antigen binding site. However, antigen-binding specificity could potentially be altered by receptor editing at the immature B cell stage. 6. A patient is deficient in Artemis. How would this defect affect his immune function? Why? (3) Artemis cleaves the hairpin structure at the coding ends during V(D)J recombination. Deficiency in Artemis stalls the recombination reaction and prevents the maturation of T and B cells....
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- Spring '09