Immune system

• Antigens help the immune system identify:

  • Pathogens
  • Abnormal body cells
  • Toxins
• Antigen- A molecule that triggers an immune response from lymphocytes
• Where are phagocytes made

  Bone marrow
• Where do phagocytes travel?

  The capillaries
• Neutrophils - Engulf and digest pathogens

  Type of phagocyte
• Macrophages- Punch holes in bacteria or stick proteins to the outside of the bacteria to make them more appealing for neutrophils to destroy

  Type of phagocyte
• Phagocytosis - Engulfing solid particles using the cell membrane
• Phagocytosis steps

  1. Pathogen recognised as having non self antigens. Pathogen attaches to phagocyte by surface receptors
  2. Pathogen engulfed by phagocyte by endocytosis to form a phagosome
  3. Lysosomes fuse to phagosome to form a phagolysosome and release H202 and HCL and digestive enzymes in to pathogen to digest
  4. Harmless products excreted by exocytosis or used by phagocyte
• Antibody

  Used by immune system to Identify and neutralize foreign objects
• Pathogen

  A microorganism that causes disease
• What type of response is phagocytosis

  Non-specific
• Antigen presenting cell (APC)

  When a phagocyte presents the pathogen that it engulfed antigens on their own cell membrane which stimulates T helper cells
• Two parts of specific immune response


  Cell mediated response- Involves T lymphocytes which target pathogens

  Humoral response- Involved B lymphocytes which target pathogens
• Cell mediated immune response

  1. Phagocytosis taken place, pathogenic antigens presented on cell surface membrane
  2. T cells respond to the cell
  3. T helper cells respond first, they have receptors which fit exactly to the presented antigens
  4. This activates T cells and they begin to differentiate and recruit other T cells and activate B cells
• T helper

  Stimulates lots of cells:

  Cytotoxic T cells

  B cells

  Phagocytosis

  Memory T cells
• Cytotoxic T cells

  Kill infected cells through the release of an enzyme
• Clonal selection

  When the T helper cells bind to the antigen presented by APC which activates B cells.

  The B cells divide by mitosis (clone themselves) to form plasma cells and memory cells
• Plasma cells

  Produce antibodies that are complimentary to the antigens
• Memory cells

  Stay in the blood stream circulating

  If in contact with the antigen they divide to form plasma and memory cells
• Features of Primary immune response

  Not many initial B cells to make the antibody, and the antibodies only survive in the bloodstream for a few days
• Features of the secondary immune response

  Produce antibodies much more quickly and new memory cells enter bloodstream to provide long term immunity from reinfection of the pathogen
• What are antibodies made up of

  A quaternary protein structure

  Two heavy and two light chains
• Dark blue - constant region

  Connection between heavy chain and light chain - Hinge region

  Lighter colours - Variable regions

  Lines in between two heavy chains- Disulphide bridges

  
• Vaccines - A way of introducing antigens of a dead or weakened pathogen into the body to stimulate the production of antibodies and memory cells