Immune system

• Our bodies are dark, wet, nutrient-dense, and filled with microorganisms
• Immune system


  The body's defense system
• The immune system discriminates between

  • Self (e.g., human, phenotypical "me")
  • Other (e.g., non-human, phenotypical non-"me")
  • Healthy (e.g., regular cells)
  • Defective (e.g., cancer cells, defective embryo)
  • Pathogenic (e.g., viruses, bacteria, parasites)
• First line of defense includes

  • Physical barriers
  • Chemical barriers
  • Mechanical barriers
• In case of breach

  1. Detect

  2. Signal

  3. Recruit

  4. Destroy
• Antigens


  A marker that tells your immune system whether something in your body is harmful or not.
• Leukocytes


  White blood cells
• Cytokines


  Signals to communicate
• Types of immunity


  • Innate immunity
  • Adaptive immunity
• Innate immunity features


  • Immediate (mins-to-hours)
  • Non-specific
  • Inflammation
  • Antigen-presenting cells
  • No or little memory
• Adaptive immunity features


  • Slow (days-to-weeks)
  • Specific
  • Cell-mediated immunity
  • Antibody-mediated immunity
  • Robust memory
• Types of immune responses

  • Cell-mediated immunity
  • Humoral immunity
• Cell-mediated immunity


  Does not involve antibodies, Phagocytosis, Cytotoxic T-lymphocytes, Cytokine release
• Humoral immunity


  Involves antibodies, Complement system activation, Antitoxin release, Bacteriolysins, "Molecule-based"
• Major barriers


  • Physical barriers (skin, mucous membranes)
  • Mechanical barriers (tears, coughing, sneezing, GI motility, ciliated epithelia)
  • Chemical barriers (enzymes, pH, lysozymes, existing microbiome)
  • Other (temperature, diet, behaviour)
• Lymphoid tissues


  • Tonsils
  • Thymus
  • Bone marrow
  • Spleen
  • Lymph nodes
  • Skin
  • Gut lymphoid tissues
• Tonsils


  Uptake airborne and ingested pathogens for early detection and signaling
• Thymus


  Matures T lymphocytes
• Bone marrow


  Produces most leukocytes including B lymphocytes
• Spleen


  Acts as a reservoir for white blood cells and carries out blood-filtering functions
• Thymus gland


  A two-lobed organ located in the thorax just above the heart, size peaks in adolescence and then undergoes atrophy. Produces white blood cells and peptides
• T cells


  Derived from bone marrow precursors, will mature in the thymus, only antigen-reactive thymocytes will proliferate, all non-reactive cells undergo apoptosis (selection)
• Leukocyte types


  • Granulocytes
  • Agranulocytes
  • Phagocytes
  • Antigen presenting cells (APCs)
• Granulocytes


  • Basophils
  • Eosinophils
  • Neutrophils
• Basophils


  Circulate and regulate inflammation and the innate immune response
• Eosinophils


  Degranulate to release ROS', enzymes, growth factors, and cytokines, fight parasites and amplify allergic responses
• Neutrophils


  A type of white blood cell that is an important part of the immune system and helps the body fight infection. Phagocytic, release cytokines, and mediate inflammation
• Agranulocytes


  • Monocytes
  • Lymphocytes
• Monocytes


  Precursors to macrophages, liver Kupfer cells, brain microglia, and osteoclasts in bone
• Lymphocytes


  Found in lymph and blood, making up 20-40% of all white blood cells, multi-functional, including T cells and B cells
• Self-tolerance


  Our immune system must be calibrated to avoid self-destruction, lymphocytes responsive to self-antigen will not proliferate and die by apoptosis, lymphocytes non-responsive to self-antigen will proliferate
• Hygiene hypothesis


  Exposure to non-self antigens in early life may strength lifelong immunity
• Innate immunity


  A default feature of the body and maintains a level of baseline defense
• Innate immunity features


  • Chemotaxins
  • Pyrogens
  • Acute-phase proteins
  • Histamine
  • Complement proteins
• Chemotaxins


  Promote migration of cells to the site of release
• Pyrogens


  A type of cytokine release by monocytes and macrophages to increase body temperature (fever)
• Acute-phase proteins


  Promote fever, recruit cells, and active complement system (includes C-reactive protein)
• Histamine


  Triggers G-protein coupled histamine receptors to active chloride channels, regulates blood vessel diameter, analgesia, itch trigger, gastric acid secretion, food intake, sleep/wake cycle
• Complement proteins


  Enhance clearance of microbes
• Adaptive immunity


  Acquired, displaying features of learning and memory