Communicable diseases, disease prevention and the immune system

• Sources of some drugs

  Penicillin (antibiotic) - mould growing on melons

  Docetaxel/Paclitaxel (breast cancer treatment) - Yew trees

  Aspirin (pain-killer and anti-inflammatory) - willow bark

  Prialt (pain-killer) - Cone snail venom

  Vancomycin (Antibiotic) - Soil fungus

  Digoxin (Heart drug) - Foxgloves
• Pandemic

  Mass spread of disease on an international level
• Epidemic

  Mass spread of disease on a national level
• Principles of vaccination

  1. The pathogen is made safe in one of a number of ways so that antigens are intact but there is no risk of infection. Vaccines may contain:

  - Killed or inactivated bacteria and viruses, e.g. whooping cough

  - Attenuated strains of live bacteria or viruses, e.g. rubella

  - Toxin molecules that have been altered and detoxified, e.g. tetanus

  - Isolated antigens extracted from the pathogen, e.g. flu

  - Genetically engineered antigens, e.g. Hepatisis B

  2. Small amounts of the safe antigen, known as the vaccine, are injected into the blood

  3. The primary immune response is triggered by the foreign antigens and your body produces antibodies and memory cells as if you were infected with a live pathogen

  4. If you come into contact with the live pathogen, the secondary immune response is triggered
• Passive immunity

  the short-term immunity that results from the introduction of antibodies from another person or animal.
• Active immunity

  A form of acquired immunity in which the body produces its own antibodies against disease-causing antigens.
• Immunisation

  Vaccination
• Artificial immunity

  acquired through a medical procedure such as a vaccine
• Natural immunity

  Immunity that is developed either through normal life processes or by inheritance
• Autoimmune disease examples

  Type 1 diabetes: affects the insulin-secreting cells of the pancreas. Can be treated with insulin injections, pancreas transplants and immunosuppressant drugs

  Rheumatoid Arthritis: affects joins, particularly in the hands, wrists, ankles and feet. It has no cure, but can be treated with immunosuppressants, steroids, pain relief and anti-inflammatory drugs
• Clonal expansion

  the rapid multiplication of B or T cell clones after activation by an antigen after clonal selection
• Clonal selection

  The process by which an antigen selectively binds to and activates only those lymphocytes bearing receptors specific for the antigen. The selected lymphocytes proliferate and differentiate into a clone of effector cells and a clone of memory cells specific for the stimulating antigen.
• Interleukins

  proteins (cytokines) that stimulate the growth of B and T lymphocytes
• Cell-mediated immunity

  Type of immunity produced by T cells that attack infected or abnormal body cells

  1. In the non-specific defence system, macrophages engulf and digest pathogens by phagocytosis. They process the antigens from from the surface of the pathogen to form antigen-presenting cells

  2. The receptors on some of the T helper cells fit the antigens. These T helper cells become activated and produce interleukins, which stimulate more T cells to divide rapidly by mitosis. They form clones of identical activated T helper cells that all carry the right antigen to bind to a particular pathogen

  3. The cloned T cells may:

  - Develop into T memory cells

  - Produce interleukins that stimulate phagocytosis

  - Produce interleukins that stimulate B cell division

  - Stimulate the development of a clone of T killer cells specific to the presented antigen
• B memory cells

  B lymphocytes that live a long time and provide immunological memory of the antibody needed against a specific antigen.
• B effector cells

  B lymphocytes that divide to form plasma cell clones
• Plasma cells

  Cells that develop from B cells and produce antibodies and only lives for a few days, but produces many antibodies during that time.
• T regulator cells

  T lymphocytes that suppress and control the immune system, stopping the response once a pathogen has been destroyed and preventing an autoimmune response.
• T memory cells

  T lymphocytes that live a long time and are part of the immunological memory.
• T killer cells

  T lymphocytes that destroy pathogens carrying a specific antigen with perforin.
• T helper cells

  T lymphocytes with CD4 receptors on their cell-surface membranes, which bind to antigens on antigen-presenting cells and produce interleukins, a type of cytokine.
• B lymphocytes (B cells)

  lymphocytes which mature in the bone marrow and that are involved in the production of antibodies
• T lymphocytes (T cells)

  Lymphocyte that matures in the thymus and acts directly against antigens in cell-mediated immune responses.
• Antitoxins

  produced by the host body to neutralize toxins
• Agglutinins

  Causes pathogens to clump together
• How antibodies defend the body

  - The antibody of the antigen-antibody complex acts as an opsonin so the complex is easily engulfed and digested by phagocytosis

  - Most pathogens can no longer effectively invade the host cells once they are part of an antigen-antibody complex

  - Antibodies act as agglutinins, clumping pathogens together

  - Antibodies act as antitoxins
• Constant region

  A portion of the antibody that is the same throughout all antibodies and is used to bind onto phagocytes
• Hinge region

  Allows the antibody to flex
• Variable region

  That region of antibodies that varies from one antibody to another even within one class that binds to the antigen
• Antibody structure

  - Y-shaped

  - Made up of two identical long polypeptide chains called heavy chains and two much shorter identical chains called the light chains.

  - The chains are held together by disulphide chains and there are disulphide bridges within the polypeptide chains to hold them in shape

  - Has a variable region, a hinge region and a constant region
• Antibodies (immunoglobulins)

  Proteins that attack foreign proteins and pathogens
• Opsonins

  Proteins that make cells more attractive to phagocytes, such as immunoglobulin
• Antigen-presenting cells

  Macrophages with antigen material on its surface
• Major Histocompatibility Complex (MHC)


  Group of genes that code for proteins found on the surfaces of cells that help the immune system recognize foreign substances.
• Stages of phagocytosis

  1) Pathogens produce chemicals that attract phagocytes.

  2) Phagocytes recognise non-human proteins on the pathogen. This is a response not to a specific type of pathogen, but simply a cell or organism that is non-self.

  3) The phagocyte engulfs the pathogen and encloses it in a vacuole called a phagosome.

  4) The phagosome combines with a lysosome to form a phagolysosome.

  5) Enzymes from the lysosome digest and destroy the pathogen.
• Phagocytosis

  A type of endocytosis in which a phagocyte engulfs pathogens for them to broken down within the cell
• Fevers

  - Normal body temperature is 37 degrees

  - When a pathogen invades your brain, cytokines trigger the hypothalamus and your temperature goes up

  - This is done because most pathogens reproduce best at or below 37 degrees and higher temperatures inhibit that and because the specific immune system works faster at higher temperatures
• Cytokines

  Small proteins, such as interferons and interleukins, that send signals and messages throughout the body
• Histamines

  Chemicals that cause inflammation and allergies.
• Inflammation

  A localized response to an injury or to the destruction of tissues