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Antigen processing and presentation

Antigen processing and presentation. Dr Jacinta Kelly. Antigen processing and presentation. Why is it needed? How does it happen? How are the pathways of endogenous and exogenous antigen kept apart? What are the consequences?. T cell receptor: antigen receptor of T cells.

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Antigen processing and presentation

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  1. Antigen processing and presentation Dr Jacinta Kelly

  2. Antigen processing and presentation • Why is it needed? • How does it happen? • How are the pathways of endogenous and exogenous antigen kept apart? • What are the consequences?

  3. T cell receptor: antigen receptor of T cells Cannot recognise antigen in solution Must have the antigen processed and presented to it Specialised molecules present antigens to T cells: MHC molecules

  4. Antigen presentation cells required

  5. 1. 3. 2

  6. TCR MHC

  7. Antigen presentation by MHC molecules • Two types of MHC molecules • MHC class I • MHC class II • Two types of T cells • CD4 T helper cells • CD8 T cytotoxic cells • Two types of antigen • Endogenous (from within the cell) • Exogenous (from outside the cell)

  8. Type of T cell activated • MHC class I activate CD8 T cytotoxic cells • Present endogenous (eg viral) antigens • Target cell is killed by CD8 cell • Any cell can become virally infected/neoplastic • Therefore: MHC class I is on all nucleated cells

  9. Ag CD8+ T cell Cell expressing MHC class I CD 8 binds 3 domain Stabilises interaction Death of target cell MHC class I Ag presentation to CD8 T cell

  10. CD8 CTL Tumour cell

  11. T cytotoxic cell Endogenous antigen MHC I TCR Death of target cell

  12. Type of T cell activated • MHC class II activate CD4 T helper cells • Present exogenous (eg bacteria) antigens • CD4 T cells upregulate all immune functions • MHC class II found only on cells that sample the extracellular environment

  13. MHC class II-CD4 T cell activation • CD4 T helper cells up regulate immune function • Stimulate M activation and phagocytosis, B cell antibody production • Help to clear exogenous antigen

  14. CD4+ T cell Cell expressing MHC class II CD 4 binds mainly 2 domain Stabilises interaction Upreglation of Immune responses MHC class II Ag presentation to CD4 T cell

  15. T helper cell macrophage TCR MHC II Exogenous antigen cytokines phagocytes antibodies Bcell

  16. Antigen: linear Protein fragments How does antigen get Into MHC binding cleft How does endogenous Ag bind MHC class I? How does exogenous ag Bind MHC class II?

  17. A question of language • Cells that express MHC class I, present endogenous ag • Are killed by CD8+ cells • Are called Target cells • Cells that express MHC class II, present exogenous ag • Activate the CD4 T cell response • Are called Antigen presenting cells

  18. Target cells: • All nucleated cells express MHC class I • Can be a target cell if virally infected/neoplastic • Antigen presenting cells • Limited number of cells express MHC class II • Must sample extracellular environment • Monocytes, MΦ, B cells

  19. Antigen processing and presentation • Separate pathways for endogenous and exogenous pathways

  20. 3 2 1 Endogenous antigen presentation

  21. 4 3 1 2 Exogenous antigen presentation

  22. Loading of antigen to MHC class I

  23. Loading of antigen to MHC class II

  24. Useful textbooks • Kuby Immunology • Cellular and molecular immunology (Abbas and Lichtman) • Janeway’s Immunobiology (Murphy, Travers, Walport)

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