MHC Genetic Polymorphism Overview
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Questions and Answers

What is the role of DQA2 and DQB2 in the MHC Class II region?

  • They are non-functional pseudogenes.
  • They only encode for proteasome subunits.
  • They are involved in encoding complement components.
  • They may have functional roles. (correct)

    • Which genes are categorized as pseudogenes in the HLA-DP subregion?

  • DPB1 and DPB2
  • DPA1 and DPB1
  • DPA2 and DPB2 (correct)
  • DPA1 and DPA2

    • What is a key feature of MHC polymorphism?

  • Polymorphism is the same as polygeny in MHC genetics.
  • It allows for identical MHC expression in all individuals.
  • It restricts the binding of peptides exclusively to one MHC class.
  • Allelic variants can differ significantly in amino acid sequences. (correct)

    • How does the polygenic nature of MHC contribute to immune response?

    <p>It enables expression of diverse peptides for T cell recognition.</p> Signup and view all the answers

    How many MHC class I molecules can typically be expressed by an individual due to polygeny and polymorphism?

    <p>6</p> Signup and view all the answers

    What is the significance of the binding cleft in MHC molecules?

    <p>It dictates peptide binding properties.</p> Signup and view all the answers

    What does co-dominant expression of allelic variants mean?

    <p>Both alleles are expressed simultaneously in heterozygous individuals.</p> Signup and view all the answers

    What overall effect do polygeny and polymorphism have on immune surveillance?

    <p>They ensure a robust defense against pathogen evasion.</p> Signup and view all the answers

    What is the role of MHC genetic polymorphism in the immune system?

    <p>It allows T cells to recognize a wide variety of peptides.</p> Signup and view all the answers

    Which statement accurately describes polygeny in MHC molecules?

    <p>It refers to the existence of multiple genes encoding functionally similar proteins.</p> Signup and view all the answers

    How does polygeny and polymorphism together enhance the immune response against pathogens?

    <p>By diversifying the types of peptides that can be presented to T cells.</p> Signup and view all the answers

    Which genes are responsible for encoding MHC class I molecules?

    <p>HLA-A, HLA-B, HLA-C</p> Signup and view all the answers

    What is the function of HLA class II molecules?

    <p>To present exogenous antigens to helper T cells.</p> Signup and view all the answers

    Which of the following HLA genes is a pseudogene?

    <p>DRB6</p> Signup and view all the answers

    Which class of MHC genes forms part of the HLA-DQ subregion?

    <p>Both B and C</p> Signup and view all the answers

    Which statement about pathogen evasion is true?

    <p>Mutation of pathogen genes can lead to immune escape.</p> Signup and view all the answers

    Study Notes

    MHC Genetic Polymorphism

    • MHC molecules exhibit genetic polymorphism, meaning variations in their structure.
    • This diversity, combined with polygeny (multiple genes for similar functions), leads to a broad spectrum of peptide presentation to T cells.
    • The arrangement of MHC genes ensures a wide variety of peptides bind to T cells.
    • This ensures all antigenic peptides are recognized, destroying pathogens.
    • Pathogens can evade detection by changing their structure.
    • MHC counteracts this through polygeny and polymorphism.

    Learning Objectives

    • Understand the basis of MHC genetic polymorphism.
    • Grasp how MHC polymorphism and polygeny allow for diverse peptide presentation.
    • Explain how polygeny & polymorphism in MHC molecules prevent pathogen evasion.

    MHC Gene Organization and Polymorphism

    • MHC genes are organized to bind a wide range of peptides.
    • This ensures all antigenic peptides are recognized and pathogens destroyed.
    • Pathogens can evade detection by mutating their structure.
    • MHC counteracts this in two ways:
      • Through polygeny
      • Through polymorphism

    Polygenic Nature of MHC

    • Polygeny: Multiple functional genes related to MHC Class I and II create proteins with different peptide-binding specificities.
    • MHC Class I and II molecules are referred to as HLA (Human Leukocyte Antigen)
    • Class I Region: Three gene loci (HLA-A, HLA-B, HLA-C) encode class I a chains. β2 microglobulin is encoded on chromosome 15.
    • Class II Region: At least three class II regions (HLA-DR, HLA-DQ, HLA-DP) exist.
    • Within the DR subregion:
      • One alpha chain gene (DRA)
      • Nine beta chain genes (DRB1-9)
      • Five of these beta chain genes (DRB2-DRB9) are pseudogenes (non-functional).
      • DRB1, DRB3, DRB4, and DRB5 encodes separate DR molecules.

    Polygenic Nature of MHC (continued)

    • The presence of these genes is restricted to specific haplotypes.
    • Haplotypes (DR1, DR51, DR52, DR8, DR53) each contain specific B genes and are key to the individuality of the immune response.

    Polygenic Nature of MHC (further details)

    • HLA-DQ Subregion: Two alpha chain (DQA1 and DQA2) and three beta chain (DQB1, DQB2, and DQB3) genes. DQB3 is a pseudogene.
    • HLA-DP Subregion: Two alpha chain (DPA1 and DPA2) and two beta chain (DPB1 and DPB2) genes. DPA2 and DPB2 are pseudogenes.
    • Other Genes in the Class II Region: Two TAP (transporter associated with antigen processing) genes and two LMP (low molecular weight polypeptide) genes. TAP and LMP genes are important for antigen presentation.

    Polygenic Nature of MHC (Class III and Ib)

    • Class III Region: Contains genes that produce complement components (C2, C4, factor B) and cytokines (TNF).
    • Class Ib Region: Encodes class I-like proteins, possibly involved in differentiation during embryogenesis.

    Polymorphic Nature of MHC

    • Polymorphism describes variation within a single MHC gene and its products.
    • MHC polymorphism increases the number of MHC molecules expressed by an individual.
    • Allelic variants of MHC proteins can differ by up to 20 amino acid residues.
    • MHC variations are restricted to the outer surface (recognized by T-cell receptors) and to the peptide-binding cleft (determines peptide binding properties).
    • MHC genes are inherited as a set of alleles (haplotype).
    • MHC molecule expression is co-dominant.
    • The number of MHC class I alleles is 6 and MHC class II varies between 6 and 8.

    Summary

    • MHC genetic polymorphism leads to diverse peptide presentation through multiple alleles.
    • Polygeny, with multiple genes, enhances the diversity of presented peptides.
    • This robust immune response accounts for pathogen evasion.
    • Polymorphism and polygeny ensure continued immune surveillance and response across individuals and populations.

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    Related Documents

    L16 Genetic Polymorphism and MHC Molecules PDF

    Description

    Explore the fascinating world of MHC genetic polymorphism and understand how it plays a crucial role in the immune system. This quiz covers the organization of MHC genes, the significance of polygeny and polymorphism, and their function in peptide presentation to T cells. Test your knowledge on how these mechanisms help prevent pathogen evasion.

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