2C.2 The immune response

• what are phagocytes?

  a type of white blood cell that engulfs pathogens.
• where are phagocytes found?

  in the blood and tissue.
• what role do phagocytes play in the immune system?

  they are the first cells to respond to a trigger.
• describe the process of phagocytosis.

  - pathogens release chemicals that attract phagocytes along a conc. gradient. - when the phagocyte reaches the pathogen it binds to the antigens complimentary receptors. - the phagocyte then engulfs the pathogen, encasing it in a phagocyclic vacuole in the cytoplasm. - lysosomes in the phagocyte fuse with the phagocyclic vacuole. - the lysosome releases lysozymes which hydrolyse the pathogen.- the soluble products are absorbed into the cytoplasm, the rest is expelled from the phagocyte.- the phagocyte presents the pathogens antigens which activates other immune system cells.
• what is an APC?

  an antigen presenting cell, phagocytes will present the pathogens antigens to trigger other immune system cells.
• what is a T cell?

  a type of WBC that has receptor proteins on its surface that bind to complimentary antigens presented by phagocytes which activates it.
• what are the two types of T cells?

  helper T cells and cytotoxic T cells.
• what happens when helper T cells are activated?

  they release chemical signals that activate and stimulate phagocytes and cytotoxic T cells.
• what happens when cytotoxic T cells are activated?

  they kill abnormal and foreign cells by releasing toxins.
• what happens when B cells are activated?

  they secrete antibodies.
• what are antibodies?

  proteins that bind to antigens to form antigen-antibody complex's.
• are antibodies specific? what does that mean?

  yes, they are complimentary so only bind to certain antigens.
• what is needed to activate B cells?

  • activated T helper cells.• the B cell binding to antigens to form antigen-antibody complex's.
• what is the process where activated B cells divide into plasma cells called?

  clonal selection.
• what cell are plasma cells identical to?

  B cells.
• what do plasma cells do?

  secrete antibodies.
• what are the antibodies secreted by plasma cells made from one B cell called?

  monoclonal antibodies.
• what do monoclonal antibodies do?

  bind to the antigens on the surface of the foreign cell to form lots of antigen-antibody complexes.
• how many binding sites do antibodies have? what does this mean?

  they have two so can bind to two pathogens at the same time.
• what is agglutination?


  when antibodies bind to 2 pathogens and clump them together.
• what is the benefit of agglutination?

  phagocytes can bind to antibodies and phagocytose many pathogens at once.
• what are antibodies made of?

  chains of amino acids.
• what does the specificity of an antibody depend on?

  variable regions, which form antigen binding sites. as each variable region has a unique tertiary structure that is complimentary to a specific antigen.
• what do all antibodies have in common?

  same constant regions.
• what are the two types of immune responses?

  cellular and humoral.
• what is the cellular immune response?

  the T-cells and other immune system cells that they interact with.
• what is the humoral response?

  B-cells, clonal selection and the production of monoclonal antibodies.
• what is the primary response?

  the immune response that results from the first exposure to an antigen.
• is the primary response immediate?

  no it takes time, the infected person will show symptoms until there is enough antibodies.
• what are memory cells?


  a long-lived lymphocyte capable of responding to a particular antigen on its reintroduction, long after the exposure that prompted its production.
• what is the secondary response?

  when pathogens renter the body, memory cells are activated and divide into plasma cells quickly.