Powerpoint

• The eye - tears & the conjunctiva, The respiratory system- mucus and cilia, The skin- sebum & sweat, The stomach- hydrochloric acid, The blood- white blood cells
• Pathogen

  Any microorganism that causes disease. E.g. bacteria, fungi, viruses or protozoa
• Antigen


  A molecule that triggers an immune response by lymphocytes. E.g. virus-infected cells, cells from other organisms, tumour cells
• Antibody


  A protein produced by lymphocytes in response to a specific antigen
• Immunity


  The means by which the body protects itself from infection
• Defence mechanisms


  • Non-specific (Response is immediate and the same for all pathogens)
  • Specific (Response is slower and specific to each pathogen)
• Non-specific defence mechanisms


  • Physical Barrier (e.g. Skin)
  • Phagocytosis
• Specific defence mechanisms

  • Cell-mediated response (T Lymphocytes)
  • Humoral response (B Lymphocytes)
• How the immune system knows not to attack body cells

  1. Any that bind to self-antigens undergo apoptosis, programmed cell death

  2. In the fetus, lymphocytes constantly collide with other cells

  3. These lymphocytes die or are suppressed

  4. There are about ten million different lymphocytes each capable of recognising a specific shape

  5. The only remaining lymphocytes are those that fit with foreign material

  6. In adults, lymphocytes in the bone marrow only encounter self-antigens

  7. Some of the lymphocytes fit the body cells receptors exactly

  8. No clones of the anti-self cells will appear in the blood

  9. Infection is rare in the womb, so the lymphocytes mainly only collide with self cells
• It is important that we recognise our own body cells (self) cells from foreign cells (non-self). If we cannot do this it can lead to destruction of our own body tissues causing autoimmune diseases such as: Type 1 Diabetes, Multiple Sclerosis, Coeliac Disease, Rheumatoid Arthritis
• To identify different cells, each cell (self and non-self) displays proteins in their cell surface membrane = antigens
• These protein molecules allow the immune system to identify: Pathogens, e.g. HIV, Non-self materials e.g. cells from other organisms of the same species, Toxins e.g. those produced by pathogens such as bacterium which causes cholera, Abnormal body cells such as cancer cells
• The immune system recognises transplant tissue as non-self, so it attempts to destroy the transplant
• To minimise rejection, donor tissues are matched as closely possible to the recipient, e.g. a close relative. Immunosuppressant drugs are also given to reduce the level of immune response that still occurs
• From what we did last lesson: There are about ten million different lymphocytes each capable of recognising a specific shape, In the fetus, lymphocytes constantly collide with other cells, Infection is rare in the womb, so the lymphocytes mainly only collide with self cells, Some of the lymphocytes fit the body cells receptors exactly, These lymphocytes die or are suppressed, The only remaining lymphocytes are those that fit with foreign material, In adults, lymphocytes in the bone marrow only encounter self-antigens, Any that bind to self-antigens undergo apoptosis, programmed cell death, No clones of the anti-self cells will appear in the blood
• Phagocyte


  Type of white blood cell which engulf pathogens. These are part of the non-specific immune system
• Lymphocyte


  Type of white blood cell responsible for the specific immune system. They become activated in the presence of antigens. There are two types, T-lymphocytes and B-lymphocytes
• Phagocytosis


  The phagocyte is attracted to the pathogen by chemoattractants, It moves towards the pathogen down a concentration gradient, The phagocyte binds to the pathogen, The phagocyte ENGULFS the pathogen forming a PHAGOSOME, Lysosomes in the phagocyte migrate towards the phagosome and FUSE with it, The lysosomes release their hydrolytic enzymes into the phagosome, and HYDROLYSE the pathogen, The breakdown products of the bacterium are absorbed by the phagocyte
• Antigen presenting cells (APCs)


  Some phagocytes that have engulfed and hydrolysed a pathogen, present the pathogen antigens on their own cell-surface membrane, They then become APCs - this can then activate the SPECIFIC immune system
• 1. Cells and Cell-Mediated Immunity

  We are learning about T-cells
• B cells

  Mature in the bone marrow, associated with humoral immunity (involving antibodies in body fluids)
• T cells

  Mature in the thymus gland, associated with cell mediated immunity (involving body cells)
• Location of Thymus gland in the lymphatic system

  The Lymphatic System
• Role of Different T-Cells

  • Cytotoxic T-cells - destroy antigen carrying cells by attaching and releasing perforin to kill them
  • Helper T-cells - attract and stimulate macrophages and promote activity of other T and B cells
  • Memory T-cells - multiply quickly if a second invasion occurs (2o response)
  • Suppressor T-cells - slow down response of cytotoxic and helper T-cells stopping immune reaction after about a week
• Antigen presenting cells (APC)

  1. lymphocytes only respond to foreign antigens presented on our own body cells
• Antigen presenting cells


  • Phagocytes which have engulfed a pathogen and presented the antigens
  • Body cells invaded by a virus - present some viral antigens
  • Transplanted cells from same species with different antigens
  • Cancer cells different from normal and present antigens
• Cell-mediated immunity


  1. Phagocyte places pathogen antigens on cell surface (APC)

  2. Specific helper T cell receptors fit the antigens, activating T cell division

  3. Cloned T-cells develop into memory cells, stimulate phagocytes, stimulate B-cells, activate cytotoxic T-cells
• Cytotoxic T-cells (Tc) kill abnormal cells and cells infected by pathogens
• Perforin


  Chemical released by cytotoxic T-cells that makes holes in cell surface membrane, killing the cell
• Antibiotics


  Used to treat bacterial infections, either by preventing bacterial reproduction or killing the bacteria
• How antibiotics work


  • Prevent reproduction of bacteria
  • Kill bacteria, e.g. by stopping cell wall building mechanism
• Antibody Production: Summary

  1. Pathogen antigens taken up by B cell

  2. B cell processes antigens and presents on surface

  3. Helper T cell attaches to B cell, activating it to divide into plasma cells

  4. Plasma cells secrete specific antibodies that bind to pathogen antigens

  5. Some B cells become memory cells for faster response to future infections
• Antibodies


  Also known as Immunoglobulins, Y-shaped protein molecules made by B lymphocytes
• Antibody Structure


  • 4 polypeptide chains (2 heavy, 2 light)
  • Variable region is the antigen binding site, constant region enables binding to cells
  • Hinge region gives flexibility to bind multiple antigens
• Antigen-antibody complex formation


  Leads to agglutination, stimulation of phagocytosis, and binding/clumping of the antigen
• Antibody-mediated immunity involves antibodies specific to bacterial antigens attaching to the antigens
• Vaccination


  A vaccine contains an antigen from a pathogen, which stimulates the immune system to produce a primary response and make memory cells. Subsequent infection by the same antigen then induces the secondary response.
• Herd immunity


  If a large proportion of the population are immune the disease has little opportunity to spread and cause an epidemic. Members of a population who are not immune are therefore protected.
• Features of a successful vaccination programme

  • Be economically available in sufficient quantities to immunise most of vulnerable population
  • Few side effects (unpleasant side-effects will discourage people)
  • Ways of producing, storing, and transporting the vaccine must be available. E.g. refrigerated transport
  • Have a means of administering the vaccine, and at the appropriate time, i.e. trained staff, vaccine centres
  • Must be possible to vaccinate vast majority of population to produce HERD IMMUNITY
• Active immunity


  Production of antibody by plasma cells, Production of B memory cells which gives long term immunity, Can take time to develop