IMM: BLOCK 2: LECTURE 3: ANTIGEN-PRESENTATION (PART 1 OF 2)
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What is the primary role of Major Histocompatibility Complex (MHC) proteins?

  • To produce antibodies against infections
  • To enhance phagocytosis by macrophages
  • To display antigen peptides to T-cells (correct)
  • To destroy pathogens directly

    • Which class of MHC is mainly expressed by professional antigen-presenting cells (APCs)?

  • MHC Class I
  • MHC Class IV
  • MHC Class III
  • MHC Class II (correct)

    • What contributes to the unique MHC pattern in individuals?

  • Polymorphism of MHC genes (correct)
  • Single allele mutations
  • Natural immunity
  • Environmental factors

    • Where is the human MHC molecule located?

    <p>Chromosome 6 (D)</p> Signup and view all the answers

    What is the significance of MHC heterozygosity in relation to HIV-1 infection?

    <p>It delays the progression to AIDS (B)</p> Signup and view all the answers

    Which of the following is true regarding tissue distribution of MHC molecules?

    <p>Microglial cells express MHC Class II (B)</p> Signup and view all the answers

    What is the result of a lack of diversity in HLA class I and class II allotypes for humans?

    <p>Increased susceptibility to viral infections (C)</p> Signup and view all the answers

    Which of the following best describes the source of MHC proteins in an individual?

    <p>Combined genetic contributions from both parents (C)</p> Signup and view all the answers

    What is the primary role of antigen presenting cells (APCs) in the immune system?

    <p>To present foreign antigens to T cells (B)</p> Signup and view all the answers

    Which type of molecule is primarily involved in the binding of peptide antigens for T cell recognition?

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

    What important function do MHC molecules serve in the immune response?

    <p>Process and present peptides to T cells (D)</p> Signup and view all the answers

    In the context of antigen presenting cells, what differentiates professional APCs from atypical or amateur APCs?

    <p>Professional APCs provide additional signals required for T cell activation (B)</p> Signup and view all the answers

    What is the significance of MHC restriction in T cell activation?

    <p>It determines which T cells can respond to specific peptide-MHC combinations (D)</p> Signup and view all the answers

    How does the immune system prevent T cells from mistakenly attacking the body’s own cells?

    <p>Through the action of professional APCs and regulatory signals (D)</p> Signup and view all the answers

    What mechanism do human cells utilize to process proteins for MHC presentation?

    <p>Degradation into small peptides (D)</p> Signup and view all the answers

    Which statement accurately describes the structure of MHC I and MHC II molecules?

    <p>MHC I molecules are composed of two chains, while MHC II has three chains (A)</p> Signup and view all the answers

    What is a key structural component of MHC class I molecules?

    <p>A membrane-bound heavy chain and β2-microglobulin (D)</p> Signup and view all the answers

    Which genetic loci are involved in the expression of MHC class I molecules?

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

    What type of cells typically express MHC class II molecules?

    <p>Antigen-presenting cells and specialized epithelial cells (A)</p> Signup and view all the answers

    How many amino acids can MHC class I molecules typically bind in their peptide cleft?

    <p>8-9 amino acids (A)</p> Signup and view all the answers

    What feature distinguishes 'nonclassical' class I molecules from classical class I molecules?

    <p>They show limited variability and tissue distribution. (C)</p> Signup and view all the answers

    What is the main function of MHC class II molecules?

    <p>To present peptide antigens to CD4+ T cells (D)</p> Signup and view all the answers

    What structural components do MHC class II molecules consist of?

    <p>A co-dominantly expressed α and β chain (A)</p> Signup and view all the answers

    Which aspect of MHC class I binding grooves contributes to polymorphism?

    <p>Slight structural variations in the binding cleft (B)</p> Signup and view all the answers

    Which does NOT correctly describe MHC class II molecules?

    <p>They can only accommodate peptides larger than 20 amino acids. (A)</p> Signup and view all the answers

    Which factor influences the binding preferences of different MHC class I molecules?

    <p>The allelic variation in the binding groove (D)</p> Signup and view all the answers

    Why is it necessary for other cells to process and present foreign antigens to T cells?

    <p>To prevent T-cells from rapidly attacking the body’s own tissues (C)</p> Signup and view all the answers

    What is the primary role of peptide-MHC (pMHC) complexes in the immune response?

    <p>To present peptide antigens for recognition by T-cell receptors (A)</p> Signup and view all the answers

    What mechanisms do human cells use to produce pathogen-derived peptides for MHC presentation?

    <p>Degradation of proteins into small peptides (D)</p> Signup and view all the answers

    Which of the following describes a characteristic of professional antigen-presenting cells (APCs)?

    <p>They efficiently process and present foreign antigens to T-cells (B)</p> Signup and view all the answers

    What does MHC restriction refer to in the context of T-cell activation?

    <p>The requirement for T-cells to recognize antigens only when presented by MHC molecules (B)</p> Signup and view all the answers

    What role do housekeeping mechanisms play in human cells regarding antigen presentation?

    <p>They help to degrade and recycle damaged proteins (C)</p> Signup and view all the answers

    How does the immune system control the activity of T-cells during antigen processing and presentation?

    <p>By having a system of checks and balances (B)</p> Signup and view all the answers

    What type of study was referred to as the “Sweaty T-Shirt” Study in the context of immunology?

    <p>A research study on scent and immune response (C)</p> Signup and view all the answers

    What is the main consequence of MHC heterozygosity in relation to immune response?

    <p>Increased flexibility in responding to various infections (A)</p> Signup and view all the answers

    Which gene regions are included in the human MHC class I gene complex?

    <p>A, B &amp; C (B)</p> Signup and view all the answers

    What is the relationship between MHC genes and tissue typing for transplants?

    <p>MHC proteins help match donor and recipient immune profiles. (A)</p> Signup and view all the answers

    What role do microglial cells have concerning MHC class II molecules?

    <p>They express MHC class II and contribute to brain immunity. (D)</p> Signup and view all the answers

    Why do humans maintain diversity in HLA class I and class II alleles?

    <p>To ensure survival against a variety of infections. (A)</p> Signup and view all the answers

    Which cells primarily express MHC class II molecules?

    <p>Professional antigen-presenting cells (APCs) (D)</p> Signup and view all the answers

    How do MHC class I and class II molecules differ in terms of cellular expression?

    <p>Class I is expressed by all nucleated cells, class II mainly by APCs. (A)</p> Signup and view all the answers

    What is a characteristic feature of MHC molecules that contributes to their function?

    <p>They exhibit high genetic polymorphism. (A)</p> Signup and view all the answers

    What is the primary structural component that distinguishes MHC class I molecules from MHC class II molecules?

    <p>MHC class I has a single membrane-bound heavy chain and a light chain. (A)</p> Signup and view all the answers

    Which amino acid length can MHC class II molecules typically accommodate in their binding groove?

    <p>18-20 amino acids (B)</p> Signup and view all the answers

    What role do the α3 domain and β2-microglobulin serve in MHC class I molecules?

    <p>They stabilize the structure of the heavy chain. (B)</p> Signup and view all the answers

    Which genetic loci are responsible for encoding MHC class II molecules?

    <p>HLA-DP, HLA-DQ, HLA-DR (A)</p> Signup and view all the answers

    Which of the following best describes the binding cleft of classical MHC class I molecules?

    <p>It is formed by α1 and α2 domains. (D)</p> Signup and view all the answers

    What defines the polymorphism observed in MHC class I molecules?

    <p>Variations in the binding groove across different allelic forms. (D)</p> Signup and view all the answers

    Which class of MHC molecules is typically expressed on all nucleated cells?

    <p>MHC class I (A)</p> Signup and view all the answers

    What type of cells predominantly express MHC class II molecules?

    <p>Professional antigen-presenting cells (APCs) (A)</p> Signup and view all the answers

    What is the function of nonclassical MHC class I molecules such as CD1d?

    <p>They present carbohydrate and peptide fragments. (B)</p> Signup and view all the answers

    What is a distinctive feature of the α and β chains of MHC class II molecules?

    <p>They combine only with others encoded within the same region. (A)</p> Signup and view all the answers

    What must occur for the activation of T cells during an immune response?

    <p>Antigens must be processed and presented to T cells with additional signals. (C)</p> Signup and view all the answers

    What is the relationship between a pathogen and MHC molecules during antigen presentation?

    <p>MHC molecules bind peptides derived from both synthesized and extracellular antigens. (D)</p> Signup and view all the answers

    How does the immune system prevent T cells from causing autoimmunity?

    <p>Other cells present foreign antigens with signals to modulate T cell activity. (C)</p> Signup and view all the answers

    What is the primary importance of MHC restriction in T cell activation?

    <p>It ensures T cells only respond to specific antigen-MHC combinations. (D)</p> Signup and view all the answers

    How are the peptides that bind to MHC molecules produced?

    <p>They are degraded from damaged or unwanted proteins within human cells. (B)</p> Signup and view all the answers

    Which statement accurately reflects the role of professional antigen-presenting cells (APCs)?

    <p>They can present both endogenous and exogenous antigens to T cells. (C)</p> Signup and view all the answers

    In what manner do atypical or amateur APCs differ from professional APCs?

    <p>Only professional APCs present antigens effectively to T cells. (D)</p> Signup and view all the answers

    What aspect of T cell activation makes it challenging to control once initiated?

    <p>Once activated, T cells become difficult to regulate and can rapidly proliferate. (A)</p> Signup and view all the answers

    What is the primary structural feature of MHC class I molecules that allows for peptide binding?

    <p>A closed peptide cleft formed between α1 and α2 domains (A)</p> Signup and view all the answers

    Which genetic loci are responsible for encoding classical MHC class II molecules?

    <p>HLA-DP, HLA-DQ, HLA-DR (D)</p> Signup and view all the answers

    What is a characteristic feature of MHC class II molecules compared to MHC class I?

    <p>They can accommodate longer peptides of 18-20 amino acids. (A)</p> Signup and view all the answers

    What distinguishes 'nonclassical' class I molecules from classical class I molecules?

    <p>Limited variability and specific tissue distribution. (D)</p> Signup and view all the answers

    Which of the following statements correctly describes the expression of MHC class I molecules?

    <p>They are co-dominantly expressed on all nucleated cells. (A)</p> Signup and view all the answers

    What is the role of the α3 domain and β2-microglobulin in MHC class I molecules?

    <p>They stabilize the structure of the peptide-binding cleft. (C)</p> Signup and view all the answers

    What type of cells primarily express MHC class II molecules?

    <p>Professional antigen-presenting cells and activated T cells. (A)</p> Signup and view all the answers

    Which aspect of MHC class I binding contributes to its polymorphism?

    <p>Structural variation in the peptide-binding groove. (B)</p> Signup and view all the answers

    Which of the following best describes the peptide-binding groove of MHC class II molecules?

    <p>It can accommodate peptides longer than those for MHC class I. (D)</p> Signup and view all the answers

    How do MHC class I and class II molecules differ in terms of their association with chains?

    <p>MHC class I consists of a heavy and a light chain, while class II consists of two similar chains. (B)</p> Signup and view all the answers

    What is a consequence of having a diverse range of HLA class I and class II alleles in humans?

    <p>It enables the immune system to better recognize a variety of pathogens. (C)</p> Signup and view all the answers

    Which statement correctly describes the role of MHC molecules?

    <p>They bind to foreign antigens and help T cells recognize infected cells. (C)</p> Signup and view all the answers

    Which cells do NOT typically express MHC class II molecules?

    <p>Nucleated somatic cells (B)</p> Signup and view all the answers

    What is the likely effect of MHC heterozygosity on the progression of diseases such as AIDS?

    <p>It delays disease progression. (D)</p> Signup and view all the answers

    Which major loci are associated with MHC class I molecules?

    <p>A, B, C (D)</p> Signup and view all the answers

    What does the presence of multiple alleles per MHC gene family provide in terms of immune system function?

    <p>It enhances the capacity to present diverse antigens. (A)</p> Signup and view all the answers

    Which is true regarding the expression of MHC class I molecules?

    <p>All nucleated cells express MHC class I molecules. (C)</p> Signup and view all the answers

    Which feature is essential for the recognition of self from non-self in the immune system?

    <p>The diversity of MHC molecules. (B)</p> Signup and view all the answers

    Study Notes

    Antigen Processing and Presentation

    • T-cells require strict regulation to avoid autoimmunity.
    • Other cells process foreign antigens and present to T-cells with additional signals required for full activation.
    • Antigens are displayed on the cell surface bound to MHC (Major Histocompatibility Complex) molecules.

    MHC: Major Histocompatibility Complex

    • MHC molecules are membrane-bound proteins that display antigen peptides to T-cells.
    • Each person has a unique MHC pattern due to parental genetic contributions.
    • MHC variability impacts the ability to fight infection as each individual's response to microbes is unique.
    • The human MHC molecule is located on chromosome 6.

    MHC Class I

    • Found on the surface of ALL NUCLEATED CELLS.
    • Composed of 45-kDa MHC class I molecules with Beta2 microglobulin (β2m).
    • MHC Class I three genetic loci (HLA-A, HLA-B, HLA-C) are highly polymorphic with >100 alleles at each locus.
    • MHC class I molecules combine with β2m creating a closed peptide cleft that binds 8-9 amino acid peptides.
    • The peptide-binding groove of different allelic forms may preferentially bind different peptides.

    MHC Class II

    • Typically expressed only on the surface of APCs (Antigen Presenting Cells), some activated T-cells, and some specialized epithelial cells.
    • Composed of a 32-38 kDa α chain and a 29-32 kDa β chain, forming a groove that accommodates 18-20 amino acid peptides.
    • Encoded within the HLA-DP, HLA-DQ, and HLA-DR regions.
    • DPα associates only with DPβ, DQα only with DQβ, and DRα only with DRβ.

    Antigen Processing and Presentation

    • T cell activation requires tight regulation to prevent uncontrolled cell-mediated immune responses and autoimmunity.
    • Cells process and present foreign antigens to T cells, ensuring a controlled immune response.

    Professional vs. Amateur Antigen Presentation

    • Professional APCs (e.g., Dendritic cells (DCs), Macrophages, B cells) are specialized cells that efficiently present antigens to T cells.
    • Amateur APCs (e.g., epithelial cells, fibroblasts, endothelial cells) can also present antigens, but are not as specialized as professional APCs.
    • Professional & amateur APCs differ in the types of antigens they present and how they present them.

    Major Histocompatibility Complex (MHC)

    • MHC is a membrane-bound protein that displays peptides to T cells.
    • MHC genes are inherited from both parents, leading to diverse MHC molecules.
    • Each MHC gene has multiple alleles, resulting in a unique MHC pattern for each individual (except identical twins).
    • MHC diversity plays a crucial role in immune system response to infections.
    • The MHC molecule is located on chromosome 6.
    • Class I gene complex (HLA-A, -B, -C), Class II gene complex (HLA-DP, -DQ, -DR).

    MHC Structure and Function: MHC Class I

    • Found on all nucleated cells.
    • Forms a closed peptide cleft between α1 and α2 domains that binds 8-9 amino-acid peptides.
    • Slight structural variations in the binding cleft allow for different peptide preferences.
    • "Nonclassical" class I molecules (HLA-E, -F, -G, -H) show limited variability and may present carbohydrates and peptide fragments.

    MHC Structure and Function: MHC Class II

    • Primarily expressed on the surface of APCs.
    • Forms a binding groove between α1 and β1 domains that can accommodate larger peptides (18-20 amino acids).
    • MHC class II α & β chains combine only with those encoded within the same region (e.g., DPα only with DPβ).

    MHC Restriction

    • T cells are restricted to recognizing peptides presented by specific MHC molecules:
      • CD8+ T cells recognize peptides presented by MHC Class I.
      • CD4+ T cells recognize peptides presented by MHC Class II.

    Sweaty T-Shirt Study

    • Demonstrated that humans can unconsciously detect and respond to other individuals' MHC genes through smell.
    • Participants preferred the scent of individuals with different MHC genes, indicating a potential evolutionary advantage in promoting genetic diversity.

    Antigen Processing and Presentation

    • T cell activation is tightly regulated to prevent unchecked immune responses
    • Cells present processed foreign antigens to T cells, requiring additional signals for recognition and full activation

    Antigen Presenting Cells (APCs)

    • Professional APCs: process and present antigens to T cells
    • Amateur APCs: express MHC molecules, but are not specialized antigen presenting cells

    MHC Molecules

    • Major Histocompatibility Complex (MHC): membrane-bound protein that presents antigen peptides to T cells
    • Encoded by genes from both parents
    • Genetically diverse (polymorphic), each person has a unique MHC profile (except identical twins)
    • Located on chromosome 6
    • Class I gene complex: HLA-A, HLA-B, HLA-C
    • Class II gene complex: HLA-DP, HLA-DQ, HLA-DR

    MHC Class I

    • Found on all nucleated cells
    • Composed of heavy chain (α) and β2-microglobulin (β2m)
    • Binds 8-9 amino acid peptide
    • Exhibits genetic polymorphism, leading to variations in peptide binding

    MHC Class II

    • Found on APCs, activated T cells, and specialized epithelial cells in the thymus and intestine.
    • Composed of α and β chains
    • Binds 18-20 amino acid peptide
    • Each gene region (DP, DQ, DR) has α and β loci: DPα binds only with DPβ, not DQβ or DRβ

    The Sweaty T-Shirt Study

    • Investigated human mate choice
    • Demonstrated potential for T cell-mediated immune responses to influence attractiveness

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    Explore the fascinating world of antigen processing and presentation in T-cells. Learn about the Major Histocompatibility Complex (MHC), its types, and its significance in immunity. This quiz covers MHC variability and its implications for individual immune responses.

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