1. The adaptive immune system uses multiple strategies to generate diversity in
ID: 204079 • Letter: 1
Question
1. The adaptive immune system uses multiple strategies to generate diversity in our ability to mount responses to a wide array of infectious microorganisms. These strategies include the generation of diverse repertoires of B-cell and T-cell antigen receptors, as well as polymorphism of MHC genes. The polymorphism of MHC genes differs from the diversity of lymphocyte antigen receptors in that:
A. It involves DNA rearrangements at multiple gene segments in the MHC locus.
B. It requires different enzymes than the RAG1/RAG2 recombinase required for antigen receptor rearrangements.
C. It results in a diverse repertoire of clonally distributed receptors on dendritic cells, rather than on lymphocytes.
D. It creates diversity between individuals in the population rather than within a single individual.
E. It does not contribute to the transplant rejection responses that occur after organ transplantation between unrelated individuals.
2. MHC polymorphism at individual MHC genes appears to have been strongly selected by evolutionary pressures. In other words, there appears to be selection for maintaining hundreds to thousands of different alleles of each MHC gene in the population. This notion is based on the observation that nucleotide differences between alleles that lead to amino acid substitutions are more frequent than those that are silent substitutions (i.e., not changing the amino acid sequence of the protein). In addition, the positions within the MHC protein where most of the allelic sequence variation occurs are not randomly distributed, but are concentrated in certain regions of the MHC protein. This latter point indicates:
A. That MHC genes are more susceptible to point mutations than to larger nucleotide deletions
B. That MHC allelic polymorphism has been driven by selection for diversity in peptide binding specificity
C. That MHC genes are more susceptible to all types of mutations than are other genes in the genome
D. That MHC polymorphism has evolved to prevent pathogens that infect non-human primates from infecting humans
3. In a mixed lymphocyte reaction, T cells from individual A make a robust response to antigen-presenting-cells from individual B, as long as the two individuals express different alleles of MHC molecules. Estimates indicate that up to 10% of the T cells from individual A may contribute to this response. If one performed this assay using responder T cells from a child and antigen-presenting cells from one parent, the result would be:
A. A massive proliferative response made by the antigen-presenting cells of the parent
B. A very weak response by the child’s T cells, involving only 0.1% of their T cells
C. The complete absence of any proliferative response by the child’s T cells
D. A robust cytolytic response that kills all of the parent’s antigen-presenting cells
E. A robust response by the child’s T cells
Explanation / Answer
Ans 1:
MHC genes are clustered into a complex and rearrangement of these genes create polymorphism.
Ans2:
Ans3 :
WeWwill observe weak response as there is less difference in MHC sequence of child and parent.
A. It involves DNA rearrangements at multiple gene segments in the MHC locus.Related Questions
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