Cell recognition & the immune system

• THE IMMUNE SYSTEM

  • INFECTION: An interaction between a pathogen and your bodies defence mechanism
  • THE IMMUNE SYSTEM: Made up of specialised cells that respond to foreign objects and protect from harm
  • DETECT: The cells detect: Toxins (harmful substances produced by pathogens), abnormal body cells (cells not functioning as normal eg cancer cells), pathogens (organisms that cause disease. Most are microorganisms eg bacteria & viruses. Some are fungi or protists), & cells from other organisms (cells from other organisms of the same species eg an organ transplant can induce an immune response)
• ANTIGENS:

  FOREIGN SIGNALS: Antigens are protein molecules (proteins & glycoproteins) with a highly specific tertiary structure and high variety that are present on the cell surface membrane of all cells. Antigen signal to the immune system if the cells are foreign, which is why organ donors are matched as closely as possible to the recipient along with immunosuppressant drugs reducing the level of the immune response
• ANTIGENS:

  • SPECIFICITY: Every cell has specific antigens. The antigens bind to complementary receptors on the cell surface membrane of the immune cells.If the antigens are foreign, this will induce an immune response
  • SELF SIGNALS: Not all antigens induce an immune response. Antigens can also signal if the cells are ‘self’ /they belong to the host organism
• ANTIGENS:

  RESPONSE: 1) Lysozymes break down foreign cells, 2)  Phagocytosis of foreign cells, 3)  Production of antibodies that bind to the antigens and inhibit the functioning of foreign cells
• Lymphocytes recognising own body cells:

  
• THE IMMUNE RESPONSE:1)PHAGOCYTOSIS: Pathogens= ingested phagocytes (type of white blood cell). The pathogens are destroyed inside them 2)ACTIVATION OF T-CELLS: Phagocytes activate T lymphocyte cells (type of white blood cell). Helper T cells & Cytotoxic T cells= T cells. The action of T cells= the cellular response 3)ACTIVATION OF B CELLS: T-cells activate B lymphocyte cells (type of white blood cell). B cells divide into plasma cells. The action of the B cells= the humoral response 4)PRODUCTION OF ANTIBODIES: Plasma cells secrete antibodies
• Antibodies= proteins that bind specifically to antigens on the cell surface membrane of pathogens
• IMMUNE RESPONSE: PHAGOCYTOSIS

  
• IMMUNE RESPONSE: T LYMPHOCYTES

  
• IMMUNE REAPONSE: B LYMPHOCYTES

  
• Lymphocytes recognising own body cells

  1. Lymphocytes constantly colliding with other cells in the fetus

  2. Infection in the fetus is rare as it's protected by the mother and placenta

  3. Lymphocytes will therefore collide almost always with the body's own material

  4. Some lymphocytes have receptors that fit the fetus' own body cells, and they die/are suppressed

  5. Only lymphocytes left are complementary to foreign/non-self material

  6. In adults, lymphocytes produced in bone marrow initially only encounter self antigens, and any complementary lymphocytes that show a response to them undergo programmed cell death (apoptosis) before they differentiate into mature lymphocytes

  7. No clones of the anti-self lymphocytes show up in the blood, leaving only lymphocytes that respond to non-self antigens
• Phagocytosis

  Involved in the immune response, takes place in phagocytes
• Detection of antigens

  Foreign antigens bind to specific receptors on the cell surface of phagocytes
• Engulfing the pathogen

  1. The phagocyte moves towards the pathogen

  2. The phagocyte cytoplasm surrounds the pathogen and the pathogen is engulfed

  3. When the pathogen is engulfed, its sealed into a phagosome (a vacuole) inside the cytoplasm
• Digestion of the pathogen

  1. Phagocytes have many organelles (lysozymes) that contain proteolytic enzymes

  2. A lysosome fuses with the phagosome and releases the proteolytic enzymes into the phagosome

  3. The enzymes break down the pathogen
• T Lymphocytes

  White blood cells that mature in the thymus gland and are involved in the cellular immune response
• 1)Detection of Antigens

  1. Foreign antigens invade the body cells

  2. Antigens taken in by phagocytes

  3. Antigens from the pathogen placed on the phagocytes' membrane
• 2)T Helper Cells

  A specific type of T cell that activates several cells including Phagocytes, T cytotoxic cells, & B cells
• 3)T Helper Cell Activation

  1. Pathogen antigens bind to complementary/ specific receptors on the cell surface of T lymphocyte cells

  2. Binding of the antigens activates the T helper cells
• 4)T Cytotoxic Cells

  T cells that are activated by T helper cells and kill abnormal cells and infected body cells by producing a protein (perforin) that makes holes in the cell surface membrane, causing the cell to die
• B lymphocytes

  White blood cells that mature in the bone marrow and are involved in the humoral immune response
• Activation of B cells

  1. T helper cells activate B cells

  2. B cells divide into identical cells (plasma cells)

  3. Plasma cells produce ~2000 antibodies per second

  4. Selection of correct B cell with complementary receptor to pathogen's antigen (clonal selection)
• Antigen entry into B cell

  Antigen enters B cell by endocytosis
• Clonal selection expansion

  1. Correct B cell divides multiple times (by mitosis)

  2. Production of many plasma cells with specific antibodies for antigens present in the body
• Antibodies

  Specific proteins on B cell surface membranes that are complementary (specific) to a specific antigen
• Antigen-antibody complex formation

  Binding of antigens to B cells causes clonal selection
• Plasma cells

  Cloned B cells that develop and secrete monoclonal antibodies into the blood plasma
• Monoclonal antibodies

  Antibodies produced by plasma cells that bind to antigens of pathogens
• Memory cells

  Cloned B cells that develop from clonal selection expansion
• Agglutination

  1. Pathogens are ' clumped ' together

  2. Pathogens are engulfed by phagocytes via phagocytosis

  3. Pathogens are destroyed
• B LYMPHOCYTES 2)DETECTION OF ANTIGENS: B cells have specific proteins (called antibodies) on their cell surface membranes. Each antibody is complementary (specific) to a specific antigen. When an antigen binds to an antibody, an antigen-antibody complex is formed. Binding of antigens to B cells also causes clonal selection
• B LYMPHOCYTES 3)PLASMA CELLS: Clonal selection -> (leads to) clonal selection expansion (the production of many plasma cells that have the specific antibodies for the antigens present in the body. The antibodies= monoclonal antibodies). The monoclonal antibodies bind to the antigens of the pathogens. The cloned B cells develops into either plasma or memory cells
• B LYMPHOCYTES 4)AGGLUTINATION: Aggulation ‘ clumps ’ the pathogens together. The pathogens are engulfed by phagocytes via phagocytosis and the pathogens are destroyed
• ANTIBODY STRUCTURE:Variable regions

  Each antibody has 2, different variable regions. The variable regions bind to specific antigens (to form the antigen-antibody complex) and each consist of a sequence of amino acids that form a specific 3d shape. One antibody can bind to 2 antigens, this allows the antigens to be clumped together in agglutination
• ANTIBODY STRUCTURE:Constant regions

  Every antibody has the same constant regions
• ANTIBODY STRUCTURE: Disulphide bridge

  Antibodies are made from 2 heavy chains & 2 light chains. The heavy chains are connected to the light chains by disulphide bridges
• ANTIBODY STRUCTURE:Hinge protein


  The hinge protein connects the variable region to the constant region
• ANTIBODY STRUCTURE:

  • Variable regions
  • Constant regions
  • Disulphide bridge
  • Hinge protein
• ANTIBODIES FUNCTION:

  • ANTIGENS: Antibodies do not destroy antigens directly, but prepare them to be destroyed. Eg the antigen as a bacterial cell:
  • AGGLUTINATION: Antibodies cause agglutination, where clumps of bacterial cells are formed, making it easier for phagocytes locate them  (as they are less spread out in the body)
  • MARKERS: Antibodies serve as markers that stimulate phagocytes to engulf bacterial cells (to which they are attached)
• USES OF MONOCLONAL ANTIBODIES:

  • TARGETED MEDICATION: Cancer cells in the body have antigens that signal the cells as abnormal. Monoclonal antibodies in cancer treatment can be used to bind specifically to the antigens on cancer cells. Cancer treatments can be harmful to many cells, but by binding specifically to cancer cells the antibodies allow the treatment to be targeted to only the cancer cells