Immune system

• Antigens are molecules that trigger an immune response by binding to specific receptors on white blood cells called lymphocytes.
• Lymphocytes can be divided into two main types: B-lymphocytes (B cells) and T-lymphocytes (T cells).
• Lymphocytes are the main type of cell involved in the adaptive immune response.
• Name the four types of microorganisms which can cause communicable diseases in animals and plants

  Bacteria

  fungi

  Protoctista

  viruses
• 2 human diseases caused by bacteria?

  bacterial meningitis

  tuberculosis
• 2 Human diseases caused by viruses?

  AIDS

  Influenza
• Name a disease caused by a protoctist.

  malaria
• What type of microorganism is responsible for athlete's foot and ringworm in animals?

  fungi
• Name two barrier defences which help prevent entry of pathogens in animals

  Skin and mucous membranes
• Name three defence mechanisms, other than barrier defences, which help prevent entry of pathogens in animals?

  Blood clotting , 

  wound repair , 

  expulsive reflexes.
• Name two chemical secretions which help prevent entry of pathogens in animals?

  Lysozymes - in tears

  stomach acid
• What do regulatory t cells do?

  suppress the immune system
• Effect of histamines on tissues (inflammatory response)?

  dilation of blood vessels causing redness, heat and increased formation of tissue fluid causing swelling
• Name two non-specific defence mechanisms which act in response to the entry of pathogens in animals?

  Phagocytosis

  fever
• What is a phagosome?

  the vesicle which encloses the pathogen after being engulfed by a phagocyte
• Phagolysozyme - when a lysozyme fuses with a phagosome
• 2 types of white blood cells involved in phagocytosis?

  neutrophils, macrophages
• what cells are involved in the humoral response?

  b cells and helper t cells
• Outline the steps of the humoral response:

  1. Naive b cell encounters and processes antigens and becomes an antigen-resenting cell
  2. A helper t cell binds to the antigen on the B cell that its presenting and releases cytokines to activate it
  3. B cell undergoes monoclonal expansion into plasma and memory B cells
  4. plasma cells produce antibodies
  5. Memory b cells are responsible for faster recognition for the 2nd immune response if the pathogen appears again as they will divide into even more plasma cells than the initial response
• Clonal expansion - activated B cells divide rapidly producing clones of identical daughter cells called plasma cells and memory b cells.
• Activation of B cells - T helper cells recognise the same antigen as the B cell and release cytokines that activate the B cell.
• Antibodies have two main functions: agglutination (clumping) and opsonisation
• what is important about agglutination?

  antibodies group up pathogen to allow for better engulfing by phagocytes
• what do cytokines do?

  attract phagocytes to the area

  released by helper t cell when binding to an antigen-presenting b cell to activate it
• what do opsonins do?

  bind to the antigens on pathogens to make it easier for phagocytes to recognise the pathogen
• neutrophils have a warped nucleus whilst lymphocytes have a round nucleus
• phagocytes bind onto a common molecular pattern on the surface of the pathogen
• when phagocytes bind onto and engulf a pathogen they release cytokines to attract more pathogens
• pathogens release chemicals which attract phagocytes as they travel up the concentration gradient of these chemicals to the source pathogens
• Killer T cells destroy cells by releasing perforin which destroys cell membranes
• autoimmune diseases causes self cells to be recognized as non-self cells which triggers an immune response
• Gives 2 examples of autoimmune diseases: arthritus and lupus
• B cells and T cells are produced in the bone marrow but T cells go on to mature in the thymus
• the cells that can become antigen presenting cells are:

  b cells and phagocytes
• outline the events of the cell mediated response

  1. naive t cell binds onto antigen on antigen presenting cell
  2. t cell divides into: more helper t cells and memory t cells
  3. stimulate b cells to under clonal expansion and stimulate killer t cells and phagocytosis
  4. memory t cells when encountering the antigen again directly divide into killer t cells
• agglutination is where antibody attaches to multiple pathogens causing them to stick together making it easier for phagocytosis
• killer T cells are responsible for killing virus infected cells by releasing perforin
• What are the 4 functions of antibodies??

  opsonization - allowing pathogens to be more recognisable and bound more easily

  agglutination - clumping pathogens together for better engulfing by phagocytes

  Anti-toxins - bind to toxic molecules to prevent them from functioning

  Destroying pathogens
• The structure of antibodies:

  • 2 heavy chains
  • 2 light chains
  • Variable region where it can change to be complimentary to antigens and various substances
  • constant region where it remains the same