Immune system
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Immune system






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Immune system Immune system Presentation Transcript

  • Defense against Disease Non-specific and specific strategies
  • Inherent Challenges
    • Constant surveillance and vigilance
    • Unpredictable invaders
  • The Enemy
    • Pathogens: microorganisms that are capable of causing disease
    • Viruses
    • Bacteria
    • Fungi
    View slide
  • Public Enemy #1 The Viruses
    • Modus Operandi
    • Dock with receptors on target cell surface
    • Insert viral DNA or RNA into host cell
    • Use host cell machinery to replicate new viruses
    • Lyse host cell and spread to nearby cells
    • Lytic vs. Lysogenic life cycles
    • Examples: smallpox, chickenpox, polio, HIV
    View slide
  • Public Enemy #2 Bacteria
    • Modus operandi
    • Set up shop in tissues but remain EXTERNAL to cells
    • Reproduce rapidly
    • Secrete exotoxins or contain endotoxins as part of cell wall
    • Examples: Escherichia coli, Clostridium botulinum, Salmonella
    Figure from Holt Biosources
  • Public Enemy #3 Fungi
    • Modus Operandi
    • Similar to bacteria-
    • reproduce rapidly
    • Damage cells directly or indirectly
    • by secreting enzymes
    • Examples: Athlete’s Foot,
      • Pneumocystis carinii (fungal pneumonia)
  • So what’s a body to do?
    • First line defenses: Nonspecific anatomical barriers and secretions that prevent entry, such as skin, saliva, tears (lysozyme), mucus, stomach acid, fever
    • Second line defenses: Inflammation
    • A nonspecific response triggered by histamine secreted by basophils when tissue is damaged
  • If all else fails… The Immune Response
    • A highly specific, long lasting response tailored to combat pathogens
    • Vocabulary:
    • Antigen - a molecule (usually carried on the surface of a pathogen) that is capable of eliciting an immune response
    • B-Lymphocytes - white blood cells that produce and secrete antibodies
    • T-Lymphocytes - white blood cells that serve as part of the cell-mediated immune response
  • Self- Nonself Recognition
    • Critical to appropriate immune system function
    • Tcells “learn” to distinguish self from non self as they mature in the thymus
    • All nucleated self cells display unique Human Leukocyte Antigens (HLA) on their Major Histocompatibility Complex (MHC) receptors
    • As T cells mature, they randomly produce and display a variety of receptors
    • Any T cell with receptors that bind to self MHC-HLA complexes will commit apoptosis
    • Only T cells that do NOT bind to self cells should emerge from the thymus and enter circulation
  • The Immune Response - Overview
  • Immune Response- Step by Step 1. Pathogen (carrying foreign antigens) enters and survives the inflammatory response 2. Some pathogens remain exposed in tissues where their antigens may be recognized by circulating B cells OR 3. Macrophages engulf pathogens and display their antigens on MHC (major histocompatibility complex) receptors. Macrophage has now become an Antigen Presenting Cell (APC)
  • Central Role of Helper T Cells
  • Humoral Immunity B cell response
    • If a circulating B cell’s receptors bind to foreign antigens, the B cell becomes activated
    • Activated B cells divide into Memory B cells and Plasma B cells
    • Plasma B cells rapidly produce and secrete antibodies (immunoglobulins)
    • Clonal selection amplifies the production of cells that produce effective antibodies
  • Figure from Clonal Selection
  • Mechanism of Antibody Function
    • Antibodies bind to antigens and aggregate pathogens for removal by macrophages
    • Antibodies disrupt function of pathogen’s surface proteins
    • Antibody-antigen complexes trigger the Complement system, a a series of enzymes carried in the bloodstream that lyse invaders
    Figure from
  • Cell-Mediated Immunity T cell Response
    • Helper T cells (a.k.a. T H or CD-4 T cells) constantly interact with macrophages
    • When T H cell finds a macrophage that is presenting antigen (APC) it becomes activated
    • Activated T H cells secrete cytokines, chemicals that stimulate both T and B cells
    • Stimulated cytotoxic T cells (a.k.a. killer or CD-8 T cells) divide rapidly, bind directly to pathogen infected cells and secrete enzymes that lyse infected cells