Micropara Lecture

• Non-specific host defense mechanisms

  Built-in or naturally occurring mechanisms of defense against pathogens and the infectious diseases they produce
• Host defense mechanisms


  Ways in which the body protects itself from pathogens
• Host defense mechanisms


  • An army consisting of three lines of defense
• Non-specific defenses


  The first two lines of defense are the ways in which the body attempts to destroy all types of substances that are foreign to it, including pathogens
• Innate (non-specific) defenses


  • Physical Barriers
  • Phagocytic Cells
  • Proteins
• Specific host defense mechanisms

  Third Line of Defense, Antibody production in response to the presence of foreign substances
• Antigens


  Foreign substances stimulating production of specific antibodies; "Ab generating substances"
• Lines of defense


  • Nonspecific Resistance
  • Specific Resistance (Responses of the Immune System)
• First line of defense

  • Intact Skin
  • Mucous Membrane and their secretions
  • Normal microbiota
• First line of defense

  • Phagocytic WBC
  • Inflammation
  • Fever
  • Antimicrobial substances
• First line of defense

  • Specialized lymphocytes B cells and T cells
  • Antibodies
• Skin


  • Epidermis consists of tightly packed cells with Keratin, a protective protein
• Mucous Membranes


  • Entrap invaders - goblet cells - sticky mucous
• Ciliary escalator


  • Microbes are trapped in mucus are transported away from the lungs
• Lacrimal apparatus


  • Washes the eye
• Saliva


  • Washes microbes off
• Urine


  • Flows out
• Vaginal Secretions


  • Flows out
• Fungistatic fatty acid in sebum

  • Inhibits growth of fungi
• Low pH (3-5) of skin


  • Inhibits growth of microbes
• Lysozyme


  • Degrades peptidoglycan, found in perspiration, tears, saliva, and tissue fluids
• Mucus membrane


  • Inhibits/kills the growth of microbes
• Lactoferrin


  • A CHON that binds iron, competes for free iron, pathogens deprived of essential nutrient (iron)
• Lactoperoxidase

  • Enzyme that produces superoxide radicals, highly reactive forms of oxygen, toxic to bacteria
• Rapidly dividing mucosal cells

  • Provide a physical barrier
• Hair, mucous membranes, and irregular chambers of the nose

  • Trap invaders
• Cilia (mucociliary covering)


  • On epithelial cells of the posterior nasal membranes, nasal sinuses, bronchi, trachea, transport trapped microbes away
• Low pH (1.2 – 3.0) of gastric juice


  • Kills microbes
• Bile


  • Causes chemical changes in bacterial cell walls and membrane making bacteria easier to digest
• Stomach acid + bile salts

  • Small intestine, relatively free of bacteria
• Alkalinity of the intestines

  • Inhibits microbial growth
• Peristalsis and the expulsion of feces

  • Removal of bacteria (50% of feces)
• Microbial Antagonism


  • Indigenous microflora preventing colonization by pathogens
• Inhibitory Capacity of Microflora


  • Competition for colonization sites
  • Competition for nutrients
  • Production of substances that kill other bacteria
• Second line of defense

  Where the pathogens able to penetrate the 1st line are destroyed by non-specific cellular and chemical responses
• Second line of defense

  • Production of fever
  • Production of interferons
  • Activation of the complement system
  • Inflammation
  • Chemotaxis
  • Phagocytosis
• Transferrin


  Glycoprotein synthesized in the liver with high affinity for iron, stores and delivers iron to host cells, sequestering iron and depriving pathogens of this essential nutrient
• Fever


  Body temperature above 37.8 degrees Celsius, caused by pyrogens or pyrogenic substances that stimulate the production of fever
• Fever


  • Hypothalamus normally set at 37 degrees C, Gram-negative endotoxin cause phagocytes to release interleukin 1, Hypothalamus releases prostaglandins that reset the hypothalamus to a high temp, Body increases rate of metabolism and shivering to raise temp, When IL-1 is eliminated, body temp falls (CRISIS)
• Fever


  • Stimulates WBC (leukocytes) to deploy and destroy invaders
  • Reduces available free plasma iron, limiting growth of pathogens
  • Induces production of IL-1, causing proliferation, maturation, and activation of lymphocytes