The Immune Response

• What is the first stage of the immune response?

  Phagocytosis
• What is a phagocyte?

  A type of white blood cell that engulfs pathogens
• Where are phagocytes found in the body?

  In the blood and in tissues
• What do phagocytes recognize on pathogens?

  Foreign antigens
• What happens to the cytoplasm of a phagocyte during phagocytosis?

  It moves around the pathogen, engulfing it
• What is contained in a phagocytic vacuole?

  The engulfed pathogen
• What fuses with the phagocytic vacuole?

  A lysosome
• What do lysozymes do?

  They break down the pathogen
• What role does a phagocyte play after breaking down a pathogen?

  It presents the pathogen's antigens
• What is another name for T-cells?

  T-lymphocytes
• What do T-cells bind to?

  Complementary antigens presented by phagocytes
• What do helper T-cells do?

  Release chemical signals to activate other cells
• What do cytotoxic T-cells do?

  Kill abnormal and foreign cells
• What do B-cells produce?

  Antibodies
• What is the function of antibodies?

  Bind to antigens to form complexes
• What is clonal selection in B-cells?

  Activation of B-cells by binding to antigens
• What do activated B-cells divide into?

  Plasma cells
• What do plasma cells secrete?

  Monoclonal antibodies
• What is agglutination?

  Clumping together of pathogens
• How do phagocytes use antibodies?

  They bind to antibodies to phagocytose pathogens
• What is the general structure of an antibody?

  • Made of chains of amino acids
  • Has variable regions for antigen binding
  • Contains constant regions
  • Two binding sites for pathogens
• What are the two types of immune responses?

  • Cellular response: Involves T-cells and phagocytes
  • Humoral response: Involves B-cells and antibodies
• What happens during the primary immune response?

  The immune system activates slowly to a new antigen
• What do memory cells do after the primary response?

  They remain in the body for a long time
• What is the secondary immune response?

  A quicker, stronger response to a previously encountered pathogen
• What happens to memory B-cells during the secondary response?

  They activate and divide into plasma cells
• What do memory T-cells do during the secondary response?

  They activate and divide into the correct T-cells
• What is the outcome of the secondary response?

  The pathogen is often eliminated before symptoms appear
• How do the cellular and humoral responses interact?

  • T-cells help activate B-cells
  • Antibodies facilitate phagocytosis of pathogens