12.6 Specific immune system

• specific immune system - can target a specific pathogen, although it is slower to act
• specific immune system

  • cellular response
  • humoral response
• antigens:

  • unique molecules (glycoproteins and glycolipids) found on the surface of cells
  • antigens allow the immune system to distinguish between the body's cells (self) and foreign cells (non-self).
• antibodies

  • y-shaped glycoproteins made up of 4 polypeptide chains called immunoglobins

  2 heavy chains and 2 light chains
• antibody:

  • peptide chains are held together by disulphide bridges
  • constant region - same for all antibodies and bind to receptors on cells
  • variable region - different for each antibody as its shape is complementary to a specific antigen
  • hing region - this allows the antibody to be flexible so it can bind to multiple antigens at once
  • antibodies bind to antigens on a lock and key mechanisms, forming an antigen-antibody complex
• Antibodies role of destroying pathogens:

  • agglutination
  • neutralisation of toxins
  • prevention of pathogens binding
• agglutination of pathogens:

  • causes pathogens carrying antigen-antibody complex to clump together
  • makes it easier for phagocytes to locate pathogens and allows them to engulf a number of pathogens at once. 
  • antibodies also act as opsonins, making pathogens easily recognisable by phagocytes. 
• Neutralisation of toxins:

  • antibodies act as anti-toxins where they bind to toxins produced by pathogens
  • this binding neutralises (inactivates) the toxin to prevent them damaging body cells
• Preventing pathogens binding to cells:

  • when antibodies bind to pathogens antigens, they block cell surface receptors needed to bind to host cells
  • this means that the pathogen cannot bind to host cells
• lymphocytes - a type of white blood cell, that are produced in the bone marrow

  recognise antigen molecules on the surface of pathogens and co-ordinate an immune response against that pathogen
• B lymphocytes/B cells - mature in the bone marrow. They are involved in the humoral response where they produce antibodies found in body fluids
• T lymphocytes/T cells - mature in the thymus gland. Involved in the cellular response where they respond to antigens present presented on body cells.
• Types of T lymphocytes:

  • T helper cells
  • T killer cells
  • T memory cells
  • T regulator cells
• T helper cells:

  • These cells have receptors on their cell surface that bind to complementary antigens on APC's. 
  • They produce interleukins (a type of cytokine) which stimulate B cells or phagocytes.
  • T helper cells can also form memory cells or T killer cells.
• T killer cells

  • These cells destroy the pathogen by producing a chemical called perforin.
  • Perforin makes holes in the cell surface membrane, causing it to become freely permeable and causing cell death. 
• T memory cells:

  • live for a long time and are part of the immunological memory
  • if they meet an antigen a second time, they divide rapidly to form a hig number of clones of T-killer cells that destroy the pathogen.
• T regulator cells:

  • These cells suppress the immune system after pathogens have been destroyed.
  • This helps to prevent the immune system from mistakenly attacking the body cells. 
• Types of B lymphocytes:

  • plasma cells
  • B effector cells
  • B memory cells
• B lymphocytes:

  • These cells have antibodies on their cell-surface membrane that bind to complementary antigens.
  • On doing so, they engulf the antigens and display them on their cell-surface to become antigen-presenting cells.
  • Once activated, B cells can divide into plasma cells and memory cells. 
• Plasma cells:

  • produce antibodies to a specific antigen and release them into the circulation
  • short lifespan
• B effector cells:

  • divide to form plasma cell clones
• B memory cells:

  • remain in the blood for a long time, providing immunological memory
  • They rapidly divide if the body is re-infected by the same specific pathogen. 
• stages of cellular response/cell mediated:

  1. Macrophages engulf pathogens and display their antigens on the cell surface. They are now known as antigen-presenting cells (APC's)
  2. T helper cells with complementary receptors bind to these antigens.
  3. T helper cells become activated and produce interleukins (stimulating phagocytosis) and divide by mitosis to form genetically identical clones
  4. cloned T cells develop into T memory cells, T killer cells and stimulate B cells to divide
• humoral response:

  • response to pathogens found in the blood stream, mainly bacteria and fungal
  • anti-bodies are produced that are soluble in the blood, tissue and lymph fluid
  • B cells have anti-bodies on their surface and will bind to the complementary antigens on pathogens membrane
  • B cells will engulf the pathogen and present the antigen on its surface (APC)
• Humoral response steps:

  1. B cell engulfs pathogen, presents its antigens on the membrane becomes APC.
  2. Activated T helper cells bind to B cell (APC), activation of this B cell - clonal selection
  3. interleukins produced by activated T helper cells activate B cells
  4. activated B cell divides to form plasma & memory cell clones - clonal expansion
  5. cloned plasma cells produce & secrete specific antibody which is specific to antigen on pathogen's surface.
  6. memory cells circulate blood, ready to divide if the body is re-infected by same pathogen. 
• clonal selection - The B cell with the correct antibody is selected for cloning (by being activated by a T helper cell).
• clonal expansion - The division of specific B cells to produce genetically identical clones. 
• primary immune response - This takes place when the body is exposed to a pathogen for the first time. This response is slow and the infected individual experiences symptoms of the disease. 
• secondary immune response - This takes place when when the body has been exposed to the same pathogen before. This response is much faster and stronger and pathogens are destroyed before any symptoms appear.
• autoimmune diseases:

  • Sometimes the immune system cannot recognise 'self' antigens and starts to attack them.
  • leads to the breakdown of healthy tissues
  • immunosuppressant drugs can be used
• autoimmune diseases

  • type 1 diabetes
  • rheumatoid athriritus
  • lupus
• type 1 diabetes - autoimmune disease

  • immune system attacks the insulin secreting cells of the pancreas
  • insulin injections, pancreas transplants, immunosuppressant drugs.
• rheumatoid arthritis - autoimmune disease

  • immune system attacks cells in the joints, causing pain and inflammation
  • no cure
  • anti-inflammatory drugs, steroids, immunosuppressants and pain relief
• lupus - autoimmune disease

  • immune system attacks cells in the connective tissues, causing inflammation. 
  • no cure
  • anti-inflammatory, steroids and immunosuppressants