IMMUNE SYSTEM

• Phagocytosis

  1. Neutrophil is attracted to pathogen by cell signalling molecules
  2. Neutrophil binds to pathogen with specific receptors on its cell surface, which bind to pathogen antigens
  3. Phagocyte extends plasma membrane around pathogen
  4. Phagosome becomes surrounded by lysosomes (migrate towards it)
  5. Lysosomes fuse with phagosome to form a phagolysosome, hydrolytic enzymes digest the pathogen
  6. Digested substances are reused by the neutrophil
• What are the four types of T lymphocytes?

  T helper, T cytotoxic, T suppressor, T memory
• T helper (Th)

  binds to antigens presented on body cells, stimulates many other responses
• T cytotoxic (Tc)

  kills abnormal or infected body cells 'T killer'
• T suppressor (Ts)

  stops response once infection is cleared
• T memory (Tm)

  stay in blood long term, provide immunity
• T Lymphocytes response

  1. Infection with pathogen
  2. Phagocytosis, partially digests pathogen
  3. Phagocyte presents pathogen on the plasma membrane
  4. Th cells with specific receptor binds to antigen CLONAL SELECTION
  5. Rapid mitosis to make genetically identical cells CLONAL EXPANSION
  6. Cloned Th cells then: Stimulate B lymphocytes to divide, stimulate phagocytes to destroy pathogens by phagocytosis, stimulate Tc to kill infected cells, some differentiate into Tm to provide long term immunity
• B lymphocyte activation

  1. Antigens drain into lymphatic system and bind to receptor on a specific B cell
  2. B cell processes antigens and present them on its cell surface CLONAL SELECTION
  3. Th activates B cell, CLONAL EXPANSION, differentiation into B memory cells and plasma cells
• Plasma cells

  Secrete antibodies into blood plasma, primary immune response
• Memory cells

  Circulate in blood and tissue fluid, rapidly divide when encounter antigen
• Describe primary response

  Clonal selection, clonal expansion, differentiation, plasma cells
• Describe secondary response

  B/T memory cells already in blood plasma, (no clonal selection), clonal expansion, differentiation, plasma cells make antibodies
• Antibodies

  Each have two identical binding sites which are complementary to a specific antigen

  • variable region- antigen binding site
  • constant region- receptor binding site
  • hinge region
  • heavy chain
  • light chain
  • disulfide bridges
• Antibodies: Agglutination

  Clumps of pathogen formed, easier for phagocytes to locate, limits pathogen function
• Antibodies: Marker

  Stimulate phagocytes to engulf the pathogen they are attached to
• Antibodies: Act as antitoxins


  Bind to toxins produced by pathogens which act as antigens, are neutralised
• mAbs production

  • mouse is injected with antigen, produces B/T memory lymphocytes
  • lymphocytes collected from mouse and fused with a tumor cell
  • this produces a hybridoma cell, which can divide rapidly and produce a high volume of antibodies
  • hybridoma cells separated under a microscope, each cell cultured to form a clone
  • clones tested to see if they produce the right antibody
  • required clone is grown at large, antibodies extracted from growth medium
• Functions of mAbs: Targeting medication


  • mAbs are produced specific to antigens on cancer cells
  • given to a patient, attach themselves to receptors on cancer cells
  • block chemical signals that stimulate uncontrolled growth
• Functions of mAbs: Medical diagnosis


  • much faster than conventional diagnosis
  • can use mAbs to measure level of antigens in a sample of blood
• Functions of mAbs: Pregnancy testing


  • hCG hormone binds to mAbs, forms a hCG antibody-colour complex
• Direct mAb therapy


  antibodies bind directly to cancer cells and block chemical signals that stimulate their growth
• Indirect mAb therapy


  antibodies bind to cancer cells but also have either radioactive or cytotoxic drugs attached to destroy cancer cells
• What diseases can mAbs be used to diagnose?

  Influenza, hepatitis, chlamydia, prostate cancer
• ELISA Assays

  
  

  1. Sample (e.g. blood) is adhered to a surface (e.g. slide), washed to remove excess (so it doesn't stick to the surface)
  2. Specific antibody is added, binds to antigen, excess washed off
  3. Second antibody is added and binds. this is attached to an enzyme.
  4. Substrate is added, colour change occurs when enzyme breaks down substrate
  5. High absorption = high colour intensity
• Ethical issues of mAbs

  production involves the use of live mice, some deaths have been caused by trials/ tests
• Why do we need vaccinations?

  To stop the spread of pathogens
• What is an epidemic?

  Rapid spread of a pathogen through a high proportion of the population
• What is a pandemic?

  An infectious disease which spreads rapidly across the continents
• Vaccinations

  • stimulate an immune response to give us immunity
  • causes our immune system memory cells which make antibodies
• Vaccination types: Whole live organisms

  Not as harmful as real ones, similar antigens so antibodies are just as effective
• Vaccination types: Harmless/ live attenuated


  Living weakened versions of the pathogen
• Vaccination types: Dead pathogen

  Inactivated vaccines by killing the pathogen with chemicals, heat, or radiation
• Vaccination types: Preparation of antigens


  These can contain between 1-20 types of antigens
• Vaccination types: Harmless toxin


  Inactivate toxins by treating them with formalin making them safe for use in vaccines
• Vaccine types: DNA/RNA vaccines


  Still in developmental stages, some body cells take up the DNA and start making the pathogens antigens from it
• Active immunity

  When your immune system makes its own memory cells after being stimulated by an antigen
• Natural immunity


  achieved through natural processes
• Artificial immunity

  Achieved through medical intervention
• Passive immunity


  When you are given antibodies made by a different organism
• What are the four types of immunity?

  Artificial active, natural active, artificial passive, natural passive