SPGBIO2_L6

• Immune system


  The body's line of defense against diseases or infections
• Types of immune system


  • Innate
  • Adaptive
• Innate Immune Response


  1. Always the first response to infection

  2. Acts fast but never changes from exposure to exposure
• Components of innate immune response


  • Barrier defenses (skin, mucous membranes, secretions)
  • Internal defenses (phagocytic cells, natural killer cells, antimicrobial proteins, inflammatory response)
• Barrier defenses


  The skin, mucous membranes and secretions are the first line of defense against infection
• It is important to wash hands with soap and water frequently
• The body reacts through mucous secretions and the saliva contains antimicrobial agents
• Internal defenses of innate immune response


  Phagocytic cells, natural killer cells, antimicrobial proteins (interferons, complement system), inflammatory response (histamines, mast cells, cytokines)
• Adaptive Immune Response


  Involves the recognition of traits specific to particular pathogens using a vast array of receptors
• Components of adaptive immune response


  • Humoral response (antibody production)
  • Cell mediated response (cytotoxic cells)
• Humoral response


  Production and secretion of antibodies or immunoglobulins against specific antigens
• Cell mediated response


  Cytotoxic cells defend the body against infection
• Development of B and T cells, memory cells and plasma cells


  Important aspects of cell mediated immune mechanism
• Lines of defense


  • First line (surface barriers)
  • Second line (innate immunity)
  • Third line (adaptive immunity)
• First line of defense


  Surface barriers that prevent the entry of pathogens into the body
• Surface barriers


  • Intact skin (protect external boundaries)
  • Mucous membranes (protect internal boundaries)
  • Release chemical secretions which restrict the growth of microbes
• Second line of defense


  Non-specific cellular and molecular responses of the innate immune system
• Innate immune defenses


  • Do not differentiate between different types of pathogen
  • Respond the same way upon every infection
• Components of innate immune defenses


  • Phagocytic leukocytes
  • Inflammatory responses
  • Antimicrobial proteins
  • Fever
• Third line of defense


  Lymphocytes that produce antibodies to specific antigenic fragments
• Adaptive immune response


  • Each B cell produces a specific antibody
  • Body has millions of different B cells capable of detecting distinct antigens
  • Helper T cells regulate B cell activation
  • B and T cells form memory cells after activation
• Pathogen


  A disease-causing agent that disrupts the normal physiology of the infected organism
• Types of pathogens


  • Viruses
  • Prions
  • Bacteria
  • Fungi
  • Parasites
• Viruses


  • Metabolically inert and incapable of reproducing independently of a host cell
  • Typically consist of an inner core of nucleic acid surrounded by a protein coat (capsid)
  • Can be either DNA-based or RNA-based
• Prions


  • Infectious proteins that have folded abnormally into a structure capable of causing disease
  • Can cause normally folded proteins to refold into the abnormal form and propagate within a host body
  • Form amyloid fibers that cause holes in the brain (spongiform encephalopathy)
• Bacteria


  • Unicellular prokaryotic cells that can reproduce quickly and compete with host cells for space and nutrition
  • Most are relatively harmless and some may form mutualistic relationships with hosts
  • Can cause disease by producing toxic compounds (exotoxins) or releasing substances when destroyed (endotoxins)
• Fungi


  • Usually attack the body surfaces, including the skin and mucous membranes
  • Can be unicellular (yeasts) or multicellular (molds)
  • Molds consist of branching filaments called hyphae that form a mass of invading threads called mycelium
• Parasites


  • Organisms that grow and feed on an organism to the detriment of the host's survival
  • Can be classed as ectoparasites (living on the surface) or endoparasites (living within the host)
  • Endoparasites include microparasites (single-cell protozoa) and macroparasites (multicellular helminthes)
• Pathogens are generally species-specific in their capacity to cause disease
• Certain pathogens may cross the species barrier and be able to infect and cause disease in a range of hosts
• Zoonotic diseases


  Diseases from animals that can be transmitted to humans
• Examples of zoonotic diseases


  • Rabies (dogs)
  • Certain strains of influenza (e.g. bird flu)
  • Bubonic plague (rats)
• Mechanisms of disease transmission


  • Direct contact
  • Contamination
  • Airborne
  • Vectors
• Inflammation


  The non-specific way the body responds when a pathogen damages body tissue
• Inflammatory response


  1. Mast cells and basophils release histamine

  2. Histamine causes vasodilation and increased capillary permeability

  3. Damaged cells release chemotactic factors to attract leukocytes
• Fever


  An abnormally high temperature associated with infection, triggered by the release of prostaglandins
• Benefits of fever


  • May reduce growth rate of microbes
  • May increase metabolic activity and activate heat shock proteins to strengthen immune response
• Cause of fever


  Activated leukocytes release pro-inflammatory cytokines that stimulate the hypothalamus to produce prostaglandins
• Surface barriers


  • Intact skin
  • Mucous membranes
• Skin


  • Protects external structures when intact
  • Consists of a dry, thick and tough region of dead surface cells
  • Contains biochemical defense agents (sebaceous glands, lactic acid, fatty acids)