Communicable Diseases and Prevention

• Lymphocytes and antibodies


  Provide the third line of defence against pathogens
• Third line of defence


  • Specific
  • Slower but more effective than non-specific immune responses
• Lymphocytes


  • A type of white blood cell
  • Smaller than phagocytes
  • Have a large nucleus that fills most of the cell
  • Produced in the bone marrow before birth
  • Travel around the body in the blood
• Types of lymphocytes


  • T-lymphocytes (T cells)
  • B-lymphocytes (B cells)
• Maturation of T-lymphocytes


  1. Immature T-lymphocytes originate in the bone marrow

  2. They move to the thymus gland in the chest, which is where they mature

  3. During the process of maturation T lymphocytes (T cells) gain specific cell surface receptors called T cell receptors (TCRs)

  4. These receptors have a similar structure to antibodies and are each complementary to a different antigen

  5. A small number of T cells have the same TCRs, these genetically identical cells are called clones

  6. T cells within each clone differentiate into different types of T cell: T helper cells, T killer cells and T regulator cells

  7. There is a very large number of different T cells with different TCRs

  8. This variation allows the T cells to recognise a wide range of foreign antigens
• T lymphocytes in the immune response


  1. Antigen presentation

  2. Clonal selection

  3. Clonal expansion
• Antigen presentation


  • Macrophages engulf pathogens and present the pathogen antigens on their own cell surface membrane
  • They become antigen-presenting cells (APCs)
• Clonal selection


  • T cells with T cell receptors that are complementary to the specific pathogenic antigen bind to the APC
  • They are the clones that have been selected for replication
  • Binding to the complementary antigens causes the T cell to be activated
• Clonal expansion


  • Activated T cells divide by mitosis to produce clones
  • There are now many T cells in the blood, all of which have specific roles
• Types of T cells


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


  • Release chemical signalling molecules known as interleukins (a type of cytokines)
  • Interleukins causes phagocyte activity to increase
  • Interleukins is needed to activate B cells
• T killer cells


  • Patrol the body in search of antigen-presenting body cells
  • Attach to the foreign antigens on the cell surface membranes of infected cells and secrete toxic substances that kill the infected body cells, along with the pathogen inside
  • Perforins secreted by T killer cells punch a hole in the cell surface membrane of infected cells, allowing toxins to enter
• T regulator cells


  • Down-regulate the host immune response by preventing T cells from attacking and killing uninfected host cells
  • Shutting down the immune system once the body is cleared of the pathogen
• T memory cells


  Remain in the blood, meaning that if the same antigen is encountered again the process of clonal selection will occur much more quickly