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Pathogen Recognition: Immune Responses at a Glance

Explore the intricate immune responses against pathogens, from innate defenses like phagocytic cells to adaptive immunity involving antibodies and T cells. Learn about antigen recognition and the role of various immune cells.

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Pathogen Recognition: Immune Responses at a Glance

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  1. Recognition of traits specific to particularpathogens, using a vastarray of receptors Recognition of traits sharedby broad ranges ofpathogens, using a smallset of receptors • • Pathogens(such as bacteria,fungi, and viruses) Barrier defenses: INNATE IMMUNITY(all animals) SkinMucous membranesSecretions Internal defenses: Phagocytic cellsNatural killer cellsAntimicrobial proteinsInflammatory response • Rapid response Humoral response: ADAPTIVE IMMUNITY(vertebrates only) Antibodies defend againstinfection in body fluids. Cell-mediated response: Cytotoxic cells defendagainst infection in body cells. • Slower response

  2. Pathogen PHAGOCYTICCELL Vacuole Lysosomecontainingenzymes

  3. Interstitialfluid Bloodcapillary Adenoid Tonsils Lymphaticvessels Thymus Lymphatic vessel Tissuecells Lymphatic vessel Peyer’spatches(smallintestine) Spleen Lymphnodes Appendix(cecum) Lymphnode Masses ofdefensive cells

  4. Pathogen Splinter Movementof fluid Macro-phage Signalingmolecules Mastcell Phagocytosis Capillary Neutrophil Redblood cells

  5. Antigen receptors Mature B cell Mature T cell

  6. Antigen-binding site Antigen-binding site Disulfidebridge V V V V Variable regions C C B cellantigenreceptor Constant regions C C Lightchain Transmembraneregion Heavy chains Plasmamembrane B cell Cytoplasm of B cell

  7. Antigenreceptor Antibody B cell Epitope Antigen Pathogen (a) B cell antigen receptors and antibodies Antibody C Antibody A Antibody B Antigen (b) Antigen receptor specificity

  8. Antigen-bindingsite T cellantigenreceptor Variableregions V V Constantregions C C Transmembraneregion Disulfidebridge  chain  chain Plasmamembrane T cell Cytoplasm of T cell

  9. Displayedantigenfragment T cell T cell antigenreceptor MHC molecule Antigenfragment Pathogen Host cell (a) Antigen recognition by a T cell Top view Antigen fragment MHCmolecule Host cell (b) A closer look at antigen presentation

  10. 4 3 2 1 DNA ofundifferentiatedB cell V37 V39 J4 V38 V40 J2 J5 J1 J3 C Intron Recombination deletes DNA betweenrandomly selected V segment and J segment DNA ofdifferentiatedB cell V37 V39 J5 V38 C Intron Functional gene Transcription V39 J5 pre-mRNA Intron C RNA processing mRNA J5 V39 Cap Poly-A tail C V V V Translation V C C C C Light-chain polypeptide C V Antigen receptor Constantregion Variableregion B cell

  11. B cells thatdiffer inantigenspecificity Antigen Antigenreceptor Antibody Plasma cells Memory cells

  12. 1 2 3 Antigen-presentingcell Antigen fragment Pathogen Class II MHC molecule Accessory protein Antigen receptor Helper T cell   Cytokines Cell-mediatedimmunity Humoralimmunity   B cell Cytotoxic T cell

  13. 3 1 2 Cytotoxic T cell ReleasedcytotoxicT cell Accessoryprotein Dyinginfected cell Antigenreceptor Perforin Class I MHCmolecule Gran-zymes Pore Infectedcell Antigenfragment

  14. 3 1 2 Antigen-presentingcell Pathogen Antigenfragment B cell Memory B cells Class IIMHCmolecule  Accessoryprotein Cytokines Antigenreceptor Activatedhelper T cell Plasma cells Helper T cell Secretedantibodies

  15. Activation of complement system and poreformation Opsonization Neutralization Complement proteins Antibody Formation of membraneattack complex Bacterium Virus Flow of waterand ions Pore Antigen Foreigncell Macrophage

  16. Histamine IgE Allergen Granule Mast cell

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