Cell recognition and immune response

• What is the first step of phagocytosis?

  Dead cell or pathogen release toxins that attract the phagocyte - this is called chemotaxis.
• What is the second step of phagocytosis?

  Receptors on the phagocyte attach to the pathogen's antigen.
• What is the third step of phagocytosis?

  The phagocyte engulfs the pathogen and encloses it in a phagosome.
• What is the fourth step of phagocytosis?

  Lysosomes begin to move to the phagosome and fuse with it.
• What is the fifth step of phagocytosis?

  The lysosomes release hydrolytic enzymes called lysozymes into the phagosome, hydrolysing the pathogen.
• What is the sixth step of phagocytosis?

  The soluble products after the hydrolysis of the pathogen are absorbed by the phagocyte and the antigens are presented on the cell membrane of the phagocyte, causing it to become an APC.
• Where do B-Cells mature?

  Bone marrow
• Where do T-Cells mature?

  Thymus
• What type of immune response is phagocytosis?

  Non-specific
• What is a pathogen?

  A foreign microorganism that causes disease by infection.
• What are lymphocytes?

  A type of white blood cell.
• Which lymphocytes are responsible for the cell mediated response?

  T cells
• Which lymphocytes are responsible for the humoral response?

  B cells
• T cells have specific t cell receptors that are similar to antibodies and are complementary to one antigen.
• What is the first step of cell mediated immunity?

  Phagocyte engulfs pathogen, causing it to become an APC.
• What is the second step in cell mediated immunity?

  The Helper T-cell with the specific receptors to the APC antigens binds to the APC (phagocyte)
• What is the third step of cell mediated immunity?

  The T-cell is stimulated to divide by mitosis, producing many clones.
• What do the cloned T-cells from cell mediated immunity do?

  Become memory cells circulating in the blood, activate cytotoxic T-cells and destroys infected cells by producing perforin.
• What do cytotoxic T-cells secrete?

  Cytokines
• What are cytokines?

  Cell signaling molecules.
• What stimulates B-cells to divide?

  T cells
• Where are B-cells most concentrated?

  Lymph nodes and the spleen
• As B-cells mature, the genes coding for antibodies are changed to code for different antibodies.
• Each type of B-cell can only make one type of antibody molecule.
• B-cells divide by repeatedly by mitosis (clonal expansion) in response to a specific antigen.
• During the clonal expansion of B-cells, which two types of cells are produced?

  Plasma cells and memory cells.
• What is agglutination?

  Clumping antigens together
• What do plasma cells secrete?

  Antibodies
• What is the first step of humoral immunity?

  Antigen of pathogen bind to specific B-cell and taken into the B-cell via endocytosis.
• What is the second step of humoral immunity?

  Antigens that have been taken in via endocytosis are processed and presented on the B-cell surface.
• What is the third step of humoral immunity?

  The antigens on the B-cells attract helper T-cells and they bind.
• What is the fourth step of humoral immunity?

  The binding of the helper T-cell stimulates the B-cell to divide by mitosis (clonal expansion) which produces plasma cells and memory cells.
• What is the fifth step of humoral immunity?

  Plasma cells secrete antibodies that are complementary to the antigens on the pathogen
• What is the sixth step of humoral immunity?

  The antibodies bind to the pathogen's antigens, restricting it (this is the primary response)
• What is the seventh step of humoral immunity?

  The memory cells circulate in the humor and will divide into plasma cells in response to a reinfection (this is the secondary response)
• How many polypeptide chains are in an antibody?

  Four
• What are the polypeptide chains in antibodies held together by?

  Disulphide bridges
• What are the variable regions of antibodies?

  Where the antibodies bind to specific antigens. Each antibodies variable regions have unique tertiary structures that cause them to be complementary to the antigens
• How do antibodies work?

  Agglutination, neutralising toxins and preventing viruses from entering host cells.
• What is antigenic variability?

  When pathogens can form different strains that have different antigens (usually caused by mutations in genetic material).