topic 2

• Phagocytosis


  The process by which a cell engulfs and digests a particle or pathogen
• Phagocytes


  • Found in the blood and tissues
  • Detect chemicals, debris, or abnormal cells
  • Move towards the detected substances
• Phagocytosis


  1. Phagocyte receptors bind to pathogen

  2. Phagocyte changes shape to engulf pathogen

  3. Pathogen contained in phagosome

  4. Lysosome fuses with phagosome

  5. Lysosomal enzymes destroy pathogen

  6. Phagocyte becomes antigen presenting cell
• Lysosome


  Vesicle containing enzymes that can destroy pathogens
• Lysozyme


  Enzyme in lysosomes that can hydrolyze and destroy pathogens
• Phagocytosis is a non-specific immune response, meaning it responds the same way to any detected non-self substance
• Phagocytes can engulf and destroy abnormal cells, transplants, and pathogens
• After destroying a pathogen, the phagocyte becomes an antigen presenting cell
• T lymphocytes


  Also called T cells, involved in the specific immune response
• T cells


  • Mature in the thymus
  • Involved in the cell-mediated immune response
• Specific immune response


  Response to an exact antigen or cell surface molecule
• Antigen presenting cells (APCs)


  Any cell that presents a non-self antigen on their cell surface membrane
• Types of APCs


  • Infected body cells with viral antigens
  • Phagocytes like macrophages after engulfing pathogens
  • Cells of a transplanted organ
  • Abnormal cells like cancer cells
• APCs trigger the B cell-mediated response
• Cell-mediated response


  Response of T cells to antigens presented on the surface of cells
• Cell-mediated immune response


  1. Pathogen engulfed by phagocyte

  2. Antigen presented on APC surface

  3. Helper T cells bind to antigen on APC

  4. Helper T cells activate and divide

  5. Helper T cells stimulate B cells, phagocytes, or become memory/cytotoxic T cells
• Cytotoxic T cells


  Also called killer T cells, can destroy abnormal or infected cells
• Cytotoxic T cells


  • Release perforin protein that creates pores in the cell membrane of infected/abnormal cells, causing them to die
• Cytotoxic T cells destroy infected cells to prevent further virus replication and spread
• Sore throat from a cold is caused by cytotoxic T cells destroying infected cells in the throat
• B lymphocytes


  Also known as B cells, lymphocytes which are white blood cells involved in the specific immune response
• Humoral response


  The response involving B cells and antibodies
• The term 'humoral' comes from the olden days term for body fluids, 'humor', because antibodies are soluble and transport around in the blood and other bodily fluids
• 1. cell activation


  • B cells have approximately 10 million different antibodies on their surface, complementary to 10 million different antigens
  • When a B cell collides with its complementary antigen, it takes in the antigen by endocytosis and presents it on its cell surface membrane
• Clonal expansion and differentiation (clonal selection)

  1. B cell removes antigen

  2. B cell presents antigen on cell surface

  3. B cell collides with helper T cell receptor

  4. B cell undergoes clonal expansion to create large numbers of identical B cells

  5. B cells differentiate into plasma cells and memory B cells
• Plasma cells


  Able to make antibodies
• Memory B cells


  Can divide rapidly into plasma cells if re-infected with the same pathogen
• Primary response


  First time B cell takes in antigen, some become plasma cells making antibodies and some become memory cells
• Secondary response


  Memory B cells rapidly differentiate into plasma cells making large quantities of antibodies, allowing rapid destruction of pathogen before symptoms appear
• Antibodies


  • Quaternary structure proteins made up of 4 polypeptide chains
  • Variable region binds to specific antigen
  • Constant region is always the same
• Agglutination


  1. Antibodies bind to antigens, creating antigen-antibody complexes

  2. Antibodies twist and flex to bind to multiple antigens

  3. Results in clumping together of antigens and antibodies, making it easier for phagocytes to locate and engulf
• Humoral response involves B lymphocytes responding to foreign antigens, undergoing clonal selection to release monoclonal antibodies
• Immune system


  Able to recognize the difference between healthy self cells, infected/unhealthy self cells, and non-self cells
• Lymphocytes


  • Cells that can identify non-self cells
• Cell surface molecule


  Unique identifying marker for each cell type
• Antigen


  The identifying molecule on the cell surface
• Types of cells/substances the immune system can identify

  • Pathogens (bacteria, fungi, viruses like HIV)
  • Transplanted organ cells
  • Abnormal body cells (e.g. cancer cells)
  • Toxins
• Development of lymphocytes


  1. Lymphocytes complementary to self-cell antigens are destroyed or suppressed during fetal development

  2. Remaining lymphocytes are complementary to non-self antigens
• Autoimmune diseases are caused by lymphocytes attacking self cells
• Antigen variability


  Pathogens can mutate, changing the shape of their antigens, rendering previous immunity ineffective