IID

• Positive selection in T cell development occurs in the thymus and selects for T cells capable of interacting with major histocompatibility complex (MHC) molecules appropriately.
• Lymphatic system


  Network of vessels complementary to the circulatory system that transfer lymph
• Cytokines


  Signalling molecules that recruit neutrophils to the site of injury or infection
• Lymph


  Fluid that absorbs extra fluid and pus from interstitial fluid and blood
• Immunity


  Body’s ability to resist or eliminate potentially harmful foreign materials or abnormal cells
• Lymph nodes


  Small organs scattered within the lymphatic system that contain macrophages which engulf pathogens that enter the lymph
• Immune system


  Internal defence system that recognises and either destroys or neutralises materials that are not “normal self”
• Primary lymphoid organs

  Organs that produce special immune cells called lymphocytes (i.e., the thymus and bone marrow)
• Innate immunity


  Set of immune defences that are non-specific in recognition of pathogens and same for all types of pathogens (immediate attack)
• Lymphocytes


  White blood cells that play a key role in the immune system
• Phagocytosis


  Process in which cells engulf and digest particulate matter
• Pseudopods


  Extensions of the cytoplasm
• Adaptive/acquired immunity


  Set of immune defences that are specific in recognition of pathogens and attack specific pathogens (delayed/slower attack)
• Opsonins


  Proteins such as antibodies, interferons, or proteins from the complement system
• Complement system

  Proteins in the plasma that circulate around in the inactive state
• Immunoglobulin


  Refers to either the membrane-bound antigen receptor or free-roaming antibody produced by B cells
• Toll-like receptors


  Receptor found in mammals that binds to fragments of molecules characteristic of a set of pathogens (e.g., doubled-stranded RNA found in viruses)
• Secondary lymphoid organs

  Other lymphoid organs such as the spleen, tonsils, lymph nodes and mucous membranes
• Epitope


  The small, accessible portion of an antigen that binds to an antigen receptor
• Antibody

  Soluble form of antigen receptors secreted by B cells when a B cell antigen receptor binds to an antigen
• Interferons

  Ligands and cytokines that are secreted by virus-infected body cells to signal the new of a virus invasion in an infected cell to other cells
• B lymphocytes (B Cells)


  Immune cells that mature in the bone marrow that are responsible for the humoral immune response
• Class II MHC molecule

  MHC molecules located mainly on B cells, macrophages and dendritic cells
• Antigen presentation

  The display of the antigen fragment in an exposed groove of the MHC protein
• Antigen presenting cells

  Immune cells that display fragments of the antigens they have engulfed
• Antigen receptor

  A protein that binds to antigens such as a bacterial or viral protein
• Antigens


  Any substance that elicits a B or T cell response is an antigen; large unique molecule that triggers specific immune response against itself
• Immunisation

  The use of antigens artificially introduced into the body to generate an adaptive immune response and memory cell formation
• Effector cells


  Short-lived clones that take effect immediately against the antigen and any pathogens producing the antigen
• T lymphocytes (T cells)


  Immune cells that mature in the thymus that are responsible for the cell-mediated immune response
• Clonal selection


  Body selects which lymphocytes will divide to produce a clonal population of thousands of cells specific to a particular epitope
• Memory cells

  Clones that live on to become effector cells in a secondary infection
• Major histocompatibility complex (MHC) molecule


  Protein of the infected (host) cell that displays an antigen fragment for T cells to bind to
• Inborn immunodeficiency


  Genetic or developmental defect in the production of immune system cells or of specific proteins
• Humoral immune response


  Protects the blood and the lymph, essentially the body fluids
• Cell-mediated immune response

  Specialised T cells that destroy infected host cells
• Immunodeficiency


  Disorder in which an immune system response to antigens is defective or absent
• Autoimmune disease

  Immune system is active against particular molecules of the body
• Passive immunity


  Immune response, particularly antibodies, present in the recipient are produced by another individual
• Acquired immunodeficiency


  Exposure to chemicals or biological agents that induc