Immunology

• Non-specific immune response

  • response is immediate and the same for all pathogens
  • physical barrier e.g. Skin
  • phagocytosis
• Specific immune response

  • response is slower and specific to each pathogen
  • cell mediated response - T lymphocytes
  • humoral response - B lymphocytes
• Antigens:

  A specific protein molecule that tiggers an immune response
• Pathogen:

  A micro-organism that can potentially cause disease
• Antibodies:

  A protein secured by a specific B lymphocyte. Each one is specific to a different non-self antigen.
• B lymphocyte:

  A white blood cell that causes a humoral response to infections by secreting antibodies. Matures in the bone marrow.
• T Lymphocyte:

  A white blood cell that causes a cellular response to infection. Matures in the thymus.
• Antigen presenting cell:

  A self cell that has been infected. It presents the pathogen‘s antigens on its cell surface.
• Lysosomes:

  Organelles present large amounts inside phagocytes.

  Contain enzymes to digest the pathogen (lysozyme)
• Phagocyte:

  Type of white blood cell that ingests and digests pathogens
• Receptors on the lymphocytes surface are complementary to the pathogen’s antigens
• Self:

  Body’s own material
• Non-self:

  foreign material
• Antigen variability:

  When antigens on the pathogen changes (due to mutations in the pathogens DNA), the antigens are no longer complementary to the antibodies so you would have to undergo a primary immune response if reinfected with the pathogen.
• Phagocytosis

  1. Phagocytes is attracted to the pathogen (moves down a concentration gradient)
  2. Phagocyte binds to pathogen using receptors
  3. Phagocyte engulfs the pathogen
  4. Pathogen is now contained within the phagosome in the cytoplasm formed from its plasma membrane
  5. A lysosome fuses with the phagosome and releases lysozyme
  6. Lysozyme digests the pathogen
  7. The phagocyte takes the antigens from the pathogen which activates other immune system cells
  8. It does this by presenting the antigens on its cell surface membrane -> antigen presenting cell
• T cell mediated immunity:

  • Only responds to a cell that have presented a foreign antigen on the surface
  • e.g. from antigen presenting cell, cells from transplant, cancer cells, cells infected with a virus.
  • They do not respond to a pathogen directly or antigens in body fluids
• T cell response

  1. Antigen from antigen presenting cell binds to a specific Th cell in which simulates it .
  2. It the divides by mitosis (clonal selection and expansion)
  3. Divides into more Th cells to simulate phagocytosis, Tc cells, memory T lymphocytes and Th cells which stimulate B cells
• B cell immunity / Humoral response

  -needs to be activated by a specific Th cell

  -involves soluble antibodies in body fluid

  process:

  1. Specific Th cell activates a specific B cell
  2. Divides by mitosis (clonal selection)
  3. Differentiates into memory cells and plasma cells
  4. Plasma cells produce soluble antibodies
• Mark Scheme ans

  1. Helper T cell binds to the antigen on the antigen presenting cell
  2. This helper T cell stimulates a specific B cell
  3. B cell clone or divides by mitosis
  4. Forms plasma cells that release antibodies
• Mark scheme ans 2

  1. virus contains antigen
  2. virus engulfs by phagocyte
  3. Antigen presented on the cell surface membrane of phagocyte
  4. T helper cell binds to antigen, is activated which activates a specific B cell
  5. divides to form clones, clonal selection
  6. by mitosis
  7. plasma cells produce antibodies
  8. antibodies bind to specific antigen