Chap 2

• Innate immunity also known as

  • Non-specific immunity
  • Natural immunity
  • Native immunity
• Innate immunity

  • the first and second line of defense
  • fast response
  • prevent entry of pathogen or foreign substances
  • most of the components exists before meet with foreign substance
• Nonspecific defenses

  1. First line: Skin, mucous membrane, chemicals
  2. Second line: Phagocytosis, complement, interferon, inflammation, fever
• Specific defenses

  1. Third line: Lymphocytes and antibodies
• B cells produce antibodies against specific antigens.
• Components of innate immunity


  • Physical barriers
  • Normal flora
  • Cellular barriers
  • Chemical barriers
  • Acute inflammatory reaction & fever
• Physical barriers


  Cover or coat which wrap and protect the body from external environment
• Skin


  • Layers of epithelial cells with outer layers of dead cells and waterproof keratin - stop foreign substance from entering body
  • Keratin not affected by weak acids and bases; resistant to bacterial enzymes and toxins
  • Sweat from sweat glands contains high salt concentration - can inhibit growth of many microorganisms except the normal flora of the skin
  • Microorganisms that live all over the skin cannot get through the skin unless it is broken
• Mucous membrane


  • Moist cover lining the digestive tract, respiratory tract, urogenital tract and eyes
  • Epithelial cell secrete (produce) mucus (a viscous / thick fluid)
  • Mucus trap foreign substance that attempt to entre the body
  • Sites of secretion of other substances that contribute to body defenses
• Substances secreted by mucous membrane


  • Lysozyme-breaks down the cell wall of many bacteria
  • Acids - secreted in stomach (pH2), kills most microorganisms that enter body via food
  • Digestive enzymes and bile salts - kills microorganisms
  • Lactoferrin - found in saliva, milk and seminal fluid - protect against infections from bacteria, viruses, and fungi
  • Spermine-antibacterial substance found in semen
• Normal flora


  Microbes which live on our body but do not cause any complication or disease
• Functions of normal flora


  • Compete with pathogenic microbes and prevent invasion by these microbes
  • Can inhibit growth of bacteria and fungi which are potential pathogen by competing for nutrient, secreting toxic substances, forming bacterial layer on tissue surfaces to prevent attachment of pathogens
• Cellular barriers


  Leukocytes (white blood cells)
• Types of leukocytes


  • Phagocytes
  • Cytotoxic leukocytes
  • Inflammatory leukocytes
• Phagocytic leukocytes


  • Cells which ingest (swallow) foreign substance and destroy them
  • Examples: neutrophils, monocytes, macrophages
• Neutrophils


  • Polymorphonuclear leucocytes (PMNs) because nucleus has multiple lobes (2-5)
  • Most abundant leucocytes
  • Possess both, antibody & complement receptors
  • Highly phagocytic and actively mobile
  • Phagocytose foreign cells in bloodstream; also migrate from blood into infected tissue during early stages of infection and inflammation
• Eosinophils


  • Like neutrophil, it can be recruited to tissue and function as a phagocytes
  • Primary function is secreting the contents of eosinophilic granules which destroy and kill parasites
  • Possesses both, antibody and complement receptors
  • Phagocytic role is less important than neutrophils
  • Numbers increase during certain parasitic and worm infections and allergy reactions
• Phagocytosis


  Process of ingesting and digesting by engulfment and degradation of microbes and other foreign particulate matter by cell
• Phases of phagocytosis


  1. Identification / recognition the microbes

  2. Chemotaxis of phagocyte

  3. Adherence

  4. Ingestion of microbe

  5. Digestion of microbe
• Phagocytic receptors


  Receptors on phagocytes that bind to structures on microbes' membrane to enable recognition of foreign substances
• Types of phagocytic receptors


  • Integrins and complement receptors
  • Lectins, Adhesion Receptors
  • Activation Receptors (chemokine, Interferon-R, Toll-like)
• Phagocytosis


  Ingesting and digesting by engulfment and degradation of microbes and other foreign particulate matter by cell
• Phagocyte


  • Crystalloid granule
  • Pseudopod
  • Yeast cell
• Phases of Phagocytosis


  1. Identification/recognition of microbes

  2. Chemotaxis of phagocyte

  3. Adherence

  4. Ingestion of microbe

  5. Digestion of microbe
• Identification/recognition of microbes


  Phagocytes have receptors which bind structures on microbes' membrane that do not exist on mammalian cells' membrane, enabling recognition of foreign substances
• Phagocytic Receptors


  • Integrins and complement receptors
  • Lectins, Adhesion Receptors
  • Activation Receptors (chemokine, Interferon-R, Toll-like (TLR) and IL-1 receptors)
  • MHC Class I and II
• Chemotaxis


  Chemical attraction of phagocytes to microorganism
• Adherence


  Attachment of phagocyte's plasma membrane to the surface of the microorganism or other foreign material
• Opsonization


  Microorganism coated with certain plasma protein to promote attachment to phagocyte
• Ingestion of microbe


  1. Microorganism engulfed by extensions of the cytoplasm and cell membrane called pseudopodia

  2. Microorganism trapped within phagocytic vacuoles (phagosomes)
• Digestion


  1. Phagosome pinches off from plasma membrane and enters cytoplasm

  2. Phagosome fuses with lysosome to form phagolysosome

  3. Lysosomal enzymes digest contents

  4. Residual body moves to cell boundary and discharges waste
• Antigen-presentation


  Macrophages present peptides generated from microbe's protein to T lymphocytes
• Basophils


  • Non-phagocytic leukocytes
  • Inflammatory leukocytes that can release histamine
• Natural killer cells


  • Lymphocytes that recognize infected and stressed cells and respond by killing these cells and secreting IFN-γ
• Acute Phase Proteins


  Proteins in the bloodstream that increase during an infection, acting as opsonins and facilitating complement activation
• Interferons


  Proteins secreted by viral-infected cells that protect uninfected neighbouring cells from infection and enhance natural killer cell activity
• Complement system


  Serum and cell surface proteins that help antibodies and phagocytic cells clear pathogens
• Characteristics of complement system


  • Heat-labile, can be destroyed at 56°C or more
  • Some are proteases that become active when cleaved
  • Activity continues in a cascade
• Opsonization


  Binding of C3b (or C4b) to microbe to enhance phagocytosis
• Chemotaxis


  Complement components C3a and C5a attract and activate leukocytes