Antigen and MHC

• What is an antigen?

  A substance that reacts with antibody or sensitized T cells but may not evoke an immune response
• How does an immunogen differ from an antigen?

  An immunogen can trigger an adaptive immune response, while an antigen may not
• What is the statement that describes the relationship between immunogens and antigens?

  All immunogens are antigens, but not all antigens are immunogens
• What makes foreign substances immunogenic or antigenic?

  They provoke a humoral or cell-mediated response if recognized as foreign by the immune system
• What are hapten molecules?

  Substances with lower molecular weight that cannot induce an immune response on their own
• How can haptens stimulate an immune response?

  By binding to a carrier molecule or macromolecule
• What factors influence the immune response?

  • Age (older individuals, neonates)
  • Dose (larger doses lead to greater responses)
  • Route of inoculation (intravenous, intradermal, subcutaneous, oral)
  • Health status of the host (fatigued, malnourished, stressed)
  • Genetics (predisposition linked to major histocompatibility complex)
• What is immunogenicity?


  The ability of an immunogen to stimulate a host response
• What are the traits of an immunogen?

  • Macromolecular size (at least 10,000 Daltons)
  • Chemical composition and molecular complexity (proteins and polysaccharides are best)
  • Foreignness (ability to distinguish self from non-self)
  • Ability to be processed and presented with MHC molecules
• What are antigenic determinants or epitopes?

  Molecular shapes recognized by B or T cells
• What role do haptens play in immunogenicity?

  They create new antigenic determinants when combined with a carrier
• What is the function of a carrier in immunology?


  To give the antigen its required size
• What are autoantigens?

  Antigens that belong to the host and do not evoke an immune response
• What are alloantigens?

  Antigens from other members of the host's species capable of eliciting an immune response
• What are heteroantigens?

  Antigens from other species, such as animals, plants, or microorganisms
• What are heterophile antigens?

  Heteroantigens that exist in unrelated plants or animals but are structurally similar
• What are the differences between thymus-dependent and thymus-independent antigens?

  Thymus-Dependent Antigens:

  • Require T cell assistance
  • Induce memory cell production
  • Can stimulate different immunoglobulin classes

  
  

  Thymus-Independent Antigens:

  • Do not require T cell help
  • Cannot induce memory cell proliferation
  • Only produce IgM
• What are adjuvants?

  Substances administered with an immunogen that increase the immune response
• How do adjuvants enhance the immune response?

  By providing a leukoinflammatory response that attracts immune cells to the injection site
• What is the role of aluminum salts as an adjuvant?

  To complex with the immunogen to increase size and prevent rapid escape from tissue
• What is Complete Freund’s adjuvant composed of?

  Mineral oil, emulsifier, and killed mycobacteria
• What is the main function of the Major Histocompatibility Complex (MHC)?


  To bring antigens to the cell surface for recognition by T cells
• What are the roles of MHC in the immune system?

  1. Intercellular recognition and discrimination of self/non-self
  2. Development of humoral and cell-mediated immune responses
  3. Influence on susceptibility to disease and autoimmunity
• Where is the Human Leukocyte Antigen (HLA) complex located in humans?

  On the short arm of chromosome #6
• What are the characteristics of HLA antigens?

  1. Glycoprotein component of cell membrane
  2. Present in all nucleated cells
  3. Products of the genes of MHC
• What are Class I MHC molecules responsible for?

  Presenting endogenous antigens to CD8+ T cells
• What are Class II MHC molecules responsible for?

  Presenting exogenous antigens to CD4+ T cells
• What are the differences between Class I and Class II MHC molecules?

  Class I MHC:

  • Found on all nucleated cells (except liver, neural, sperm)
  • Binds 8 to 11 amino acids
  • Closed at both ends

  
  

  Class II MHC:

  • Found on B cells, macrophages, dendritic cells
  • Binds 13 to 18 amino acids
  • Open at both ends
• What is MHC restriction?

  The process whereby MHC controls interactions between cells
• What are the applications of HLA typing/matching?

  1. Organ transplantation
  2. Paternity testing
  3. Forensic medicine and anthropology
  4. Studies of racial ancestry and migration
  5. Diagnostic and genetic counseling
  6. Basic research in immunology
• What are the methods for detecting HLA antigens?

  Serological, cellular, and molecular approaches
• What is the lymphocyte microtoxicity method used for?

  Determination of Class I antigens
• What is the mixed lymphocyte reaction used for?

  Determination of Class II antigens
• What is PCR used for in HLA antigen detection?

  It is a molecular approach for detecting HLA antigens
• What is an antigen?

  A substance that is specifically recognized by the adaptive immune system.
• What is the difference between an antigen and an immunogen?

  An immunogen is capable of eliciting an adaptive immune response, while an antigen may not.
• What does it mean for a substance to be immunogenic?

  It means the substance can stimulate an adaptive immune response.
• Why are haptens considered non-immunogenic?

  Haptens alone cannot stimulate an immune response until they bind to a carrier molecule.
• What factors influence the immune response?

  • Age: Neonates are sensitive due to underdeveloped immune systems.
  • Dose: Larger antigens lead to greater antibody concentration.
  • Route of inoculation: Affects the portal of entry.
  • Health status: Stressed individuals have lower immune responses.
  • Genetics: Hereditary diseases can impact immune response.
• What is the minimum molecular weight for a substance to be considered a good immunogen?

  At least 10,000 Daltons.