C3

• Infectious disease causing agent


  Must be able to: 1. Colonize the host 2. Live in/on the host 3. Avoid immune response 4. Replicate using host resources 5. Exit and spread to a new host
• Innate immunity


  Non-specific response to pathogens; doesn't distinguish one pathogen from another; attempts to block and stop them all

  
• Innate immunity


  • Rapid response to pathogens because it is always there ready to battle
  • Present before any exposure to pathogens. Is effective from the time of birth
  • Short duration of response; immune response lasts for hours to a few days
  • No immune memory is established; subsequent exposure to the pathogen generates the same response

  
• Adaptive immunity


  Specific response to a particular antigen type. An antigen is a molecule (usually a protein on a pathogen) that generates antibodies

  
• Adaptive immunity


  • Slower response to pathogens; there is a lag time between exposure to the antigen and full immune response
  • Requires exposure to the antigen. Built over a lifetime of exposure
  • Longer duration of response; immunity can last months or years
  • Immune memory is built; subsequent exposure to the antigen generates an amplified response

  
• Immunity


  The ability of an organism to resist infection
• Immune systems


  • Innate Immune System
  • Adaptive Immune System

  
• Innate immune system components


  • Physical Barriers
  • Internal Defenses

  
• Physical barriers


  • Skin
  • Mucus membranes
  • Chemical secretions
  • Microbiome
  • Mechanical Actions
• Skin


  Physical barrier with chemical secretions that keep hazardous organisms and materials outside of the body
• Mucus membrane


  Continuous with the skin at body openings such as the eyes, ears, inside the nose, inside the mouth, lip, vagina, the urethral opening and the anus. Cells secrete a sticky mucus that traps microbes and particles before they can get deeper into the body
• Mechanical actions


  • Peristalsis
  • Vomiting and Diarrhea
  • Flushing of bodily fluids
• Blood clotting


  Prevents blood loss from damaged blood vessels and prevents entry of pathogens through damaged blood vessels
• Blood clotting


  1. Damage to blood vessel causes platelets to adhere

  2. Platelets accumulate and create a plug

  3. Activated platelets trigger a cascade of reactions

  4. Thrombin catalyses conversion of fibrinogen to fibrin

  5. Fibrin strands form a mesh to trap blood cells and form a clot
• Phagocytic white blood cells


  1. Detection

  2. Ingestion

  3. Fusion with lysosome

  4. Digestion

  5. Discharge
• Phagocytic white blood cells


  • Display molecules from pathogens ("antigens") on their own cell surface (to activate adaptive immunity)
  • Release chemicals that summon more white blood cells to the scene
• 1. lymphocytes


  Produce molecules called antibodies as part of the adaptive immune response

  
• Antibodies


  Y shaped proteins that are present at the end of each surface in the binding site, where an antibody attaches itself to an antigen to deactivate them

  
• Antigen


  The protein on the surface of a pathogen, a humoral response
• 1. lymphocytes


  Secrete cytokines that have an effect on other cells
• 1. cell activation


  1. Phagocytic white blood cell engulfs and digests a pathogen

  2. Phagocyte places the antigen on its cell membrane (antigen presenting cell)

  3. Helper T-cell receptor binds to the antigen presenting cell

  4. Activated helper T-cell secretes cytokines

  5. Activating B cells with antibodies complementary to the antigen

  6. Activating T cytotoxic ("killer") T cells to recognize and kill infected cells

  
• 1. cell development


  1. Multipotent blood stem cell differentiates and undergoes genetic rearrangement

  2. Immature b-cells with many differently shaped antigen receptors

  3. B-cells that bind to self-proteins are destroyed

  4. Remaining B-cells circulate as inactive cells

  5. If an antigen binds to a B-cell receptor, the B-cell divides to create clones

  6. Plasma cells secrete antibodies

  7. Memory cells provide long-term immunity

  
• Antibodies


  1. Prevent pathogens from interacting with host cells (neutralization) 2. Form clumps of cells (agglutination) 3. Form insoluble solids when bound to antigens 4. Trigger the complement system to lyse pathogens or infected cells

  
• Antibody production


  1. Pathogens with surface antigens

  2. Antigen presenting cell displays antigen

  3. Helper T-cell binds to antigen presenting cell

  4. B-cells with complementary receptors are activated

  5. Activated B-cells divide into plasma cells and memory cells

  6. Plasma cells secrete antibodies

  
• Primary immune response


  Lag between exposure and antibody production, lower total antibody production, antibody level declines rapidly

  
• Secondary immune response


  Less lag between exposure and antibody production, faster peak response, greater antibody production, antibody level remains high for longer

  
• How HIV infects a T cell


  1. HIV particle attracted to T cell receptor

  2. HIV fuses with T cell membrane

  3. Viral DNA created from RNA template

  4. Viral DNA incorporated into host cell chromosome

  5. Viral genes translated into proteins

  6. New viruses bud from host cell

  
• AIDS


  When helper T numbers decline below a critical level, adaptive immunity is lost and the body becomes progressively more susceptible to opportunistic infections
• Types of acquired immunity


  • Naturally Acquired Active
  • Naturally Acquired Passive
  • Artificially Acquired Active
  • Artificially Acquired Passive
• Vaccination


  Purposeful administration of antigenic material to produce immunity to a disease, using weakened/killed pathogens, purified proteins, or nucleic acids

  
• Vaccination


  • Stimulates adaptive immunity without developing disease symptoms
  • If infection occurs after vaccination, body reacts as if second exposure
  • Considered the most effective and cost-effective method of preventing infectious diseases
• Vaccination benefits


  • Eradication of disease from a population
  • Reduced death from disease
  • Reduced disabilities from disease
  • Decreased loss of work days due to disease
• Vaccination risks


  • Immunity sometimes less effective than natural immunity
  • Side effects of vaccination
  • Rumors about complacency around getting vaccinated
• Herd immunity


  When a large percentage of the population achieves immunity to a disease, there is far fewer chance of it spreading
• Percentage change


  Calculated as (new value - old value) / (average of new and old value) x 100