Microb Immunity


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Microb Immunity

  1. 1. Immunity to microbes
  2. 2. Overview of the immune system From Immunology, Todd & Reeves
  3. 4. Range of microbial infections protozoa viruses bacteria worms fungi
  4. 5. Normal course of a primary acute infection time Level of microbe t Resolution of adaptive response & establishment of memory Innate/induction of adaptive response infection adaptive response
  5. 6. Immunity to infection requires both innate and acquired immunity Time Level of microbe Mac - /PMN - No innate immunity Scid/RAG - no T/B cells Normal immune system
  6. 7. Innate response 1: Inflammation-PPRs Tissue dwelling macrophages recognize bacterial/viral products as ‘foreign’ via pathogen associated molecular patterns (PAMPs) PAMPs are conserved products of microbial metabolism -unique to microbes -invariant between members of a given class -vital for microbial fitness LPS found in all gram -ve bacteria Immune system has a range of pattern recognition receptors (PRRs) which recognize PAMPs
  7. 8. Lipopolysaccaride: an example of a PAMP
  8. 9. LPS defective mice C3H/HeJ sub-strain found to be insensitive to toxic shock syndrome induced by LPS Mice were also susceptible to infection by certain gram -ve bacteria Reverse genetics isentified a single point mutation in the cytoplasmic tail of a Toll like receptor
  9. 10. Toll like receptors (TLRs) Ancient conserved family of PPRs Transmembrane receptors Activation leads to induction of various genes responsible for host defense NF  B MAP Cytokine Chemokine MHC Co-stimulation TLR4 LPS
  10. 11. Ligand specificity of human TLRs
  11. 12. Innate response 2: complement alternative pro-inflammatory molecules C3a C3b C5a cell lysis classical
  12. 13. Complement activation <ul><li>C3a C5a mast cell activation </li></ul><ul><li>C3b opsonisation </li></ul><ul><li>C5a chemotaxis </li></ul><ul><li>C5b-C9 MAC-lysis </li></ul>
  13. 14. N Bacteria N Activation of complement N N N LPS TLR4 mast TNF-  IL-1 E&P selectin VCAM ICAM C3a C5a C3b N N
  14. 15. Innate response 3: role of NK cells Lymphoid origin Utilize invariant receptors Vital for early control of viral infections Recognize infection as ‘altered self’-e.g. low MHCI NK cells are ‘armed’ via IFN-  -  & IL-12 Kill altered cells via secretion of cytotoxic granules (granzyme/perforin)
  15. 16. Innate response 4: activation of APC Professional APC reside in tissues iDCs (e.g. langerhans cells) Normally endocytose extracellular antigen- tolerance Activated via: -PPRs (TLRs CD14) -necrotic cell products (HSPs) -viral infection IFN 
  16. 17. Innate response 4: activation of APC iDC mDC MHCII <ul><li>Increased synthesis of MHCII </li></ul><ul><li>Migration to secondary lymphoid organs (chemokines) </li></ul>CD80 CD86 CD40 <ul><li>Upregulation of costimulatory molecules </li></ul>ICAM-1 -2 LFA-1 <ul><li>Upregulation of adhesion molecules </li></ul>
  17. 18. GC artery vein Aquired response 1: activation of naïve lymphocytes AdM
  18. 19. mDC Acquired response 1: activation of naïve T lymphocytes Tn CD80 CD86 CD40 CD28 CD40L ICAM-1 -2 LFA-1 -3 DC sign CD2 LFA-1 ICAM-2 MHCII TCR cytokines IL-2 cytokine
  19. 20. Acquired response 2: polarization of naïve T lymphocytes B worms bacteria
  20. 21. Importance of T cell polarization: Leishmania mouse model BALB/c fatal C57BL/6 recovery
  21. 22. Th1: IFN-  TNF  Leishmania specific T cell responses Th2: IL-4 IL-10 IL-13 resistant susceptible BALB/c C57BL/6
  22. 23. Leishmania specific T cell responses resistant susceptible anti-IL-12 ab or IL-12 -/- anti-IFN-  ab of IFN-  -/- susceptible resistant anti-IL-4 ab or IL-4R -/- BALB/c C57BL/6
  23. 24. Chromatin remodeling
  24. 25. mDC Th1 MHCII TCR Acquired response 3: role of Th1 cells MHCI NK M  Tc IL-2 IFN-  Tc IFN-  NK NK M 
  25. 26. Th1 mediated destruction of Leishmania
  26. 27. Virgin B cell Th2 Acquired response 4: role of Th2 cells In T cell zone IgM production Clonal expansion Class switching Affinity maturation IgG production IL-4 IL-5 IL-10 IL-13
  27. 28. No of antigen specific T cells in efferent lymphatics time 2 5 Effector T cells migrate from the lymph node to sites of infection Tn L-selectin-(CD34) Teff VLA-4 LFA-1
  28. 29. Teff TCR INFLAMED TISSUE Teff VLA-4 LFA-1 ICAM-1 VCAM-1 MHCII Teff Afferent lymphatics  MAdCAM-1 “ addressins” +ve
  29. 30. Range of effector mechanisms used to clear microbial infections plasmodium measles typhoid Schistozome Candida G Tc G Th/ M  G Th/ M  G Th/ M 
  30. 31. Resolution of the effector response When the infection is removed: the innate system is no longer activated- inflammation subsides antigen is cleared in the form of immune complexes- stimulus for T cells is removed most effector T and B are removed- death by neglect/cytokine starvation Apoptotic cells are removed by macrophages
  31. 32. Establishment of immunological memory T B Bone marrow LN Spleen Plasma cell
  32. 33. Plasma cells provide protective memory Secretion of high affinity antibody Lifespan of months-years Re-generated by low level proliferation & differentiation of memory B cells? Plasma cell
  33. 34. B Memory B cell responses provide reactive memory Proliferate and differentiate into plasma cells in response to antigenic stimulation high Low Somatic Mut high low affinity IgG IgA IgM>>IgG isotype 10 3 1:10 4 -1:10 5 frequency secondary primary
  34. 35. Memory T cell responses Tn Tm low high Requirement for co-stimulation high low Responsiveness to pep-MHC 10 1 Relative frequency
  35. 36. Memory T cell responses Two distinct populations of memory T cells exist: -effector memory (Tem) protective memory -central memory (Tcm) reactive memory Defined by (i) absence or presence of immediate effector function (ii) expression of homing receptors to enable circulation to 2˚ lymphoid organs or non lymphoid tissues
  36. 37. lymphnodes Gut lung liver distribution high low Proliferative capacity IL-2 Th1 Th2 Tc Cytokines production days hours Effector function 2˚ lymphoid organs Sites of inflamation homing CCR7 CD62L Tcm Tem CCRs
  37. 38. Model of T cell differentiation
  38. 39. Methods used by microbes to avoid the immune response HIV sequestration H. influenzae Antigenic variation Leishmania spp. Impairment of interferon response HSV HLA expression O. volvulus Lymphocyte supression EBV Lymphocyte activation (super Ags) T. cruzi Cleavage of immunoglobulin Streptococci spp. Inhibition of chemotaxis S. aureus Resistance to complement S. mansoni disguise example Method of immune evasion
  39. 40. Overview of the immune system From Immunology, Todd & Reeves