Antigen-presenting Cell (APC),T & B Cell Activation

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Antigen-presenting Cell (APC),T & B Cell Activation
2013-11-15 11:04:32
Antigen presenting Cell

Antigen-presenting Cell (APC),T & B Cell Activation
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  1. What is the adaptive immune system also known as?
    Aquired/specific immune system
  2. What is the function of adaptive immune system?
    • Eliminates foreign substances & abnormal body cells
    • Cleans up dead cells
    • Magnifies inflammatory responses
    • Shuts down inflammatory responses
    • Activates complement
    • Regulates itself
  3. What is the initial exposure to a specific substance?
  4. Reaction time of adaptive immune system?
    >96 hours
  5. What are the stages of acquired immunity?
    • 1. Establishment of infection
    • 2. Induction of adaptive response
    • 3. Adaptive immune response
    • 4. Immunological memory
  6. What are the two branches of adaptive immunity?
    • Humoral immunity
    • Cellular immunity
  7. What happens in humoral immunity?
    • Extracellular microbes e.g. bacteria activate B cells to secrete antibody
    • Antibody attach to bacteria
    • Neutralisation occurs --> lysis (complement)
    • Leads to phagocytosis by macrophage
  8. What happens in cellular immunity?
    • Intracellular microbes e.g. virues activate APC and Th cells to produce cytokines
    • Cytokines attach to cytokine receptors --> proliferation and activation of effector cells (cytotoxic T cells, NK cells, macrophages)
    • Lysis of infected cell
  9. What are the adaptive effector responses of B cells?
    Antibodies - eliminate extracellular pathogens
  10. What are the adaptive effector responses of T cells?
    • CD4+ Helper T cells - Th1, Th2, Th3, Th17 and even Th100
    • CD8+ Cytotoxic cells
  11. What is the function of Th1?
    help CD8+ T via cytokines
  12. What is the function of Th2?
    Help B cells via cytokines
  13. What is the function of CD8+ cytotoxic T cells?
    destroy infected & altered cells
  14. What is an antigen?
    Any substance that can trigger an immune response
  15. 5 examples of antigens.
    • Pathogens: bacteria, fungi, viruses, worms
    • Foreign proteins: pollen, insect venom, transplantation antigens, antibiotics etc
    • Mainly proteins
    • Lipids & carbohydrate
    • DNA
  16. T cells can only bind to processed (chopped up)...
  17. What are processed antigens?
    • Small chemical subunits made up of amino acids
    • Known as epitopes
  18. B cells recognise epitopes within intact...
  19. What are B Cell Receptors (BCR) or T Cell Receptors (TCR)?
    • Expressed on lymphocyte surfaces
    • Bind to antigen
    • Beginning of B & T cell activation
  20. What plays a key role in B & T cell activation?
    Cytokines - act as signalling molecules between immune cells
  21. What is T cell activation initiated by?
    Interactions between antigen-presenting cells (APCs) & T cells APCs  process (chop up) intact antigen into small fragments (epitopes)
  22. What are the 3 things epitopes must be?
    • 1. Inside major histocompatibility complex (MHC) molecules
    • 2. On the APC cell surface
    • 3. Presented to the TCR on T cells
  23. What are the MCH I restriction & T cell activation?
    Present intracellular antigens to CD8+ cytotoxic T cells only
  24. What are the MCH II restriction & T cell activation?
    Present extracellular  antigens to CD4+ T cells only
  25. What are the professional APCs?
    • Dentritic cells
    • Macrophages
    • B cells
  26. What dendritic cells, macrophages and b cells do in cell activation?
    Express MHC class I & II molecules
  27. Which of the professional APCs are the best at priming naive T cells?
    Dentritic cells
  28. Where is the T cell first activated (primed)?
    • Antigen capture in tissue site by DCs
    • DCs activated & start to mature
    • DCs migrate towards lymph nodes
    • Migrating DCs mature into APC
    • DCs in lymph nodes present antigen to T cells
  29. In lymph nodes T cells "stick" to DCs using what?
    Cell Adhesion Molecules (CAMs)
  30. How are immunological synapse formed?
    • Numerous receptor-ligand interactions bing T cells to APCs
    • TCR bind to peptide in MHC
    • CD4/8 bind to MHC
    • Co-stimulatory molecules B7 (on APC) bind to CD28 (on T cells)
    • Group together to form synapses
  31. How are APC activated?
    • Pattern recognition receptors (PRRs) detect pathogens
    • Toll-like receptors (TLR) recognise specific pathogen structures
    • Activate APC
    • Co-stimulatory molecules (B7 molecules) up-regulated
  32. Professional APC's express TLRs to...
    • ensure immune system responds to pathogens & not to harmless substances
    • Activates APCs = upregulation of co-stimulatory molecules
  33. What are the two signal model of T cell activation for a full activation?
    • Signal 1: Antigen recognition
    • Signal 2: Co-stimulatory molecules on APCs
  34. What is the first signal (antigen recognition) in T cell activation for?
    Ensure that response is Ag-specific
  35. What is involved in the second signal (co-stimulatory molecules on APCs) in T cell activation?
    • B7 family = CD80 & CD86 = bind to CD28 on T cells
    • CD40 = binds to CD40L on T cells
  36. What is the key cytokine the T cell needs to make and why?
    • Key cytokine is IL-2
    • Proliferation dependent on IL-2 through autocrine pathway
  37. What are the Steps to T cell activation?
    • Pathogen activates APC
    • APC expresses co-stimulatory molecules
    • Pathogen phagocytosed
    • Pathogen processed
    • APC presents peptide in MHC to naive T cells
    • T cell activated
    • T cells leave the lymph node
  38. What happens after T cell leaves lymph node?
    • Travel to site of infection/mutated cells
    • CD8+ cytotoxic T cells seek target cells
    • Target cell must present same epitope in MHC class I molecule --> killing occurs = effector cells
  39. B cell is activation is required to initiate antibody production. What are the (3) steps?
    • B cell responds to intact antigens via the B cell receptors (BCR)
    • BCR = antibody on the B cell surface
    • B cell proliferate & differentiate into: clone of antibody-secreting plasma cells
  40. What are the (3) steps in B cells process antigens for the presentation to CD4 Th2 cells?
    • Antigen bound by B cell surface receptor
    • Antigen internalized and degraded to peptide fragments
    • Fragments bind to MHC class II & transported to cell surface
  41. B cells require 2 signals for activation what are they?
    • Signal 1: B cell binding to peptide. B cells present peptide in MHC class II molecules to CD4+ T cells
    • Signal 2: Activate CD4+ T cells --> secrete cytokines (IL-4, IL-5)

    Cytokines further activate B cells --> fully differentiate antibody-secreting B cells = plasma cells
  42. What is the priming phase of T cells?
    • APC present antigenic fragments in MHC molecules to TCR
    • T cells require 2 signals for full activation
    • 1. Antigen in MHC molecules binding to the TCR
    • 2. Activated APC express co-stimulatory molecules
  43. Where is the effector stage of T cells?
    Somewhere in the body
  44. What is the priming phase of B cells?
    • BCR attaches to epitopes still in a whole antigen
    • Process antigen for presentation to CD4+ Th cells
    • B cells require 2 signals for full activation (different to T cells)
    • 1. Epitope bind to BCR
    • 2. Cytokine secreted by activated T cells
  45. Where is the effector stage for B cells?
    Somewhere in the body