Antigens and Major Histocompatibility Complex
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What is the primary function of Class I MHC molecules?

  • Present antigen fragments derived from degraded proteins to CD8+ T lymphocytes. (correct)
  • Transport proteins across the cell membrane.
  • Present antigen fragments derived from exogenous proteins to CD4+ T lymphocytes.
  • Act as receptors for antibodies.

    • Which of the following cells do NOT express Class I MHC molecules?

  • Red blood cells (correct)
  • Neurons
  • Dendritic cells
  • Epithelial cells

    • Which molecule is NOT polymorphic and is encoded by a gene on chromosome 15?

  • ß chain
  • ß2-microglobulin (correct)
  • a chain
  • a1 domain

    • Which of the following is NOT a function of HLA-G molecules?

    <p>Presenting peptide antigens to cytotoxic T cells (B)</p> Signup and view all the answers

    What is the function of the peptide-binding site in Class I and II MHC molecules?

    <p>Binding to T cell receptors (C)</p> Signup and view all the answers

    Which of the following cells express Class II MHC molecules?

    <p>B lymphocytes (A)</p> Signup and view all the answers

    Which of the following is NOT a category of MHC genes?

    <p>Class IV (A)</p> Signup and view all the answers

    What is the primary function of the a1 and a2 domains in Class I MHC molecules?

    <p>Forming the peptide-binding site (A)</p> Signup and view all the answers

    Which type of antigen is present in other members of the same species, potentially causing immune responses in situations like tissue transplantation?

    <p>Alloantigens (D)</p> Signup and view all the answers

    What is the primary function of the MHC molecule in the immune system?

    <p>To present peptide antigens to T cells for recognition (D)</p> Signup and view all the answers

    Which of the following best describes the relationship between MHC molecules and histocompatibility?

    <p>MHC molecules are the primary determinants of histocompatibility, influencing tissue acceptance or rejection (B)</p> Signup and view all the answers

    What is the significance of the Florida Panther case study in relation to MHC?

    <p>It highlights the importance of MHC diversity in combating infectious diseases (A)</p> Signup and view all the answers

    What was the initial name given to the molecules now known as MHC molecules?

    <p>Human leukocyte antigens (HLAs) (A)</p> Signup and view all the answers

    What is the significance of the high level of polymorphism within the MHC gene system in humans?

    <p>It contributes to the diversity of the human immune system response (D)</p> Signup and view all the answers

    What is the relationship between heterophile antigens and antibodies?

    <p>Antibodies against heterophile antigens can recognize antigens from unrelated species (C)</p> Signup and view all the answers

    Which type of antigen is responsible for triggering an immune response in an individual against their own tissues?

    <p>Autoantigens (C)</p> Signup and view all the answers

    Which pathway of antigen presentation is responsible for degrading proteins and generating peptide chains that are released into the cytosol?

    <p>The class I MHC pathway (B), The endogenous pathway (D)</p> Signup and view all the answers

    What is the primary function of TAP1 and TAP2 in the class I MHC presentation pathway?

    <p>To transport antigenic peptides into the lumen of the endoplasmic reticulum (D)</p> Signup and view all the answers

    Which of the following best describes the role of MHC molecules in the immune response?

    <p>They present antigen fragments to T cells, triggering an immune response. (A)</p> Signup and view all the answers

    How does the MHC presentation pathway differ between class I and class II MHC molecules?

    <p>Class I MHC presents antigens derived from intracellular pathogens, while class II MHC presents antigens derived from extracellular pathogens. (C)</p> Signup and view all the answers

    Which of the following is a clinical application of MHC testing?

    <p>Ensuring successful tissue transplantation. (D)</p> Signup and view all the answers

    The association of HLA alleles with certain diseases suggests that:

    <p>Individuals with these HLA alleles are more susceptible to those diseases. (C)</p> Signup and view all the answers

    Which of the following steps is NOT involved in the class II MHC presentation pathway?

    <p>Proteasome degradation (C)</p> Signup and view all the answers

    What is the function of CLIP in the class II MHC presentation pathway?

    <p>It binds to the peptide-binding groove of MHC class II molecules, preventing premature peptide binding. (C)</p> Signup and view all the answers

    Flashcards

    Autoantigens

    Antigens belonging to the host that do not trigger an immune response under normal conditions.

    Alloantigens

    Antigens from other individuals of the same species that can provoke an immune response.

    Heteroantigens

    Antigens from different species including animals, plants, or microorganisms.

    Heterophile antigens

    Heteroantigens that share structural similarities across unrelated species.

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    Major Histocompatibility Complex (MHC)

    Group of molecules that determine if transplanted tissue is accepted or rejected by the host.

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    Polymorphism of MHC genes

    Genetic variability in MHC genes that helps in protection against diseases.

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    Genetic Diversity in species

    Variety of genes within a population that increases health and fitness.

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    HLA Antigens

    MHC molecules initially referred to as human leukocyte antigens, key in immune responses.

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    Class II MHC

    MHC class that presents peptides to CD4+ T cells from exogenous sources.

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    Endogenous Pathway

    Class I MHC pathway presenting internal proteins to CD8+ T cells.

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    Proteasome

    A cylindrical structure that degrades proteins and generates peptides.

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    TAP1 and TAP2

    Transporters that move peptide fragments into the endoplasmic reticulum for MHC binding.

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    Exogenous Pathway

    Class II MHC pathway presenting external proteins to CD4+ T cells after engulfing them.

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    CLIP

    A molecule that blocks the peptide-binding cleft in Class II MHC until it is removed.

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    MHC Testing

    Testing for compatibility of MHC types in tissue transplantation.

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    HLA Alleles

    Genetic variants of MHC that can influence disease susceptibility.

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    MHC Genes

    Genes that help present peptides to T cells.

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    Polymorphism in MHC

    High variability allowing diverse immune responses.

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    CD8+ T cells

    Cytotoxic T cells that recognize antigens presented by Class I MHC.

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    APCs

    Antigen presenting cells that express Class II MHC molecules.

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    HLA-G

    Nonclassical Class I MHC molecule protecting the fetus from maternal NK cells.

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    Peptide-binding site

    The groove in MHC molecules where peptides bind for presentation.

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    Study Notes

    Antigens and the Major Histocompatibility Complex

    • Antigens are categorized based on their relationship to the host.
    • Autoantigens are the host's antigens that typically do not trigger an immune response under normal circumstances.
    • Alloantigens are from other members of the same species and induce an immune response.
    • Heteroantigens originate from other species (animals, plants, or microorganisms).
    • Heterophile antigens are a type of heteroantigen that are present in unrelated organisms with similar or identical structures, leading to cross-reactivity of antibodies.
    • Blood type compatibility depends on the presence of naturally occurring antibodies that are formed after exposure to bacterial cell wall products.
    • Serological reactions, in perfect circumstances, would be completely specific, but cross-reactivity occurs in diagnostic applications.
    • Heterophile antibodies, formed during infectious mononucleosis, react with sheep red blood cells, helping to diagnose the disease.

    Major Histocompatibility Complex

    • Scientists discovered genes linked to immune responses, called human leukocyte antigens (HLAs) now MHC molecules.
    • MHC molecules determine histocompatibility, whether transplanted tissue is accepted by the recipient.
    • MHC is found on all nucleated cells in the body.
    • MHC molecules are key for both humoral and cell-mediated immunity.
    • MHC molecules carry peptide antigens for T-cell recognition.
    • Unlike B cells, T cells need MHC molecules to recognize antigens.

    Florida Panther

    • Loss of genetic diversity in the Florida panther population is a major threat.
    • Genetic diversity of MHC antigens plays a vital role in disease resistance.
    • Introduction of Texas panthers into the Florida population has helped increase genetic diversity and resilience.

    Genes Coding for MHC Molecules (HLA Antigens)

    • MHC molecules are encoded by polymorphic genes, making each person's MHC type unique.
    • MHC class I molecules (A, B, C) are located in various places on chromosome 6.
    • MHC class II molecules (DR, DQ, DP) are located in the D region of chromosome 6.
    • MHC class III molecules are located between class I and II, encoding complement proteins and cytokines.
    • Multiple alleles (variant forms) of each MHC gene exist, leading to considerable polymorphism.
    • Individuals inherit two copies of chromosome 6, with the possibility of different HLA alleles; except in homozygous cases where both alleles are the same.
    • MHC genes are inherited together in haplotypes.
    • HLA haplotypes contribute to individual variations in the immune system.

    Structure of Class I MHC Molecules

    • Class I molecules are glycoprotein dimers (~44,000Da) composed of an alpha chain and a beta-2-microglobulin chain (~12,000Da)
    • The alpha chain has three domains (a1, a2, a3), with a1 and a2 making up the peptide-binding groove.
    • B2-microglobulin is located on chromosome 15.
    • This groove holds peptides (8-11 amino acids), which play a crucial role in protein recognition.

    Expression of Class I and II MHC Molecules

    • Class I molecules are found on all nucleated cells.
    • Class II molecules are on antigen-presenting cells (APCs).
    • Class I and II MHC molecules are structurally and functionally diverse.

    Class I MHC–Peptide Presentation Pathway

    • The endogenous pathway presents peptides from proteins inside the cell.
    • Proteasomes break down proteins into peptides.
    • MHC class I molecules bind peptides inside the endoplasmic reticulum.
    • The peptide-MHC complex moves to the cell surface for presentation to cytotoxic T cells.

    Class II MHC–Peptide Presentation Pathway

    • The exogenous pathway presents peptides from proteins outside the cell.
    • Phagocytosis or endocytosis take up extracellular proteins.
    • Proteases break down antigens into peptides.
    • The invariant chain (Ii) blocks the peptide-binding groove.
    • Exchange of Ii with antigen peptides occurs within endosomes.
    • MHC class II molecules present peptides on the cell surface for presentation to helper T cells.

    Clinical Significance of MHC

    • MHC testing is crucial before transplantation to avoid rejection.
    • MHC inheritance can link to autoimmune diseases.
    • MHC molecules are essential for triggering the adaptive immune system.
    • Immune system responses are influenced by age, health, inoculation method, and genetic makeup.

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    Related Documents

    Chapter 3: Nature of Antigens and the Major Histocompatibility Complex PDF

    Description

    This quiz covers the classification of antigens and their relationships to the host, including autoantigens, alloantigens, and heteroantigens. It also discusses blood type compatibility and the role of heterophile antibodies in diagnosing diseases such as infectious mononucleosis. Test your knowledge of these fundamental immunology concepts.

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