T lymphocyte response

• What are 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
• How do T lymphocytes mature?

  • Immature T-lymphocytes originate in the bone marrow
  • They move to the thymus gland in the chest, which is where they mature
  • During the process of maturation T lymphocytes gain specific cell surface receptors called T cell receptors (TCRs)
  • These receptors have a similar structure to antibodies and are each complementary to a different antigen
  • A small number of T lymphocytes have the same TCRs, these genetically identical cells are clones.
  • T cells within each clone differentiate into different types of T cell: Th, Tk Tr
• In order to play their role in the immune response T cells need to be activated and increase in number, outline the main stages in this processes?

  Antigen presentation

  Clonal selection

  Clonal expansion
• T lymphocytes ( T cells) in the immune response?

  Macrophages engulf pathogens and present the pathogen antigens on their cell-surface membrane, they become APCs.

  T cells with T cell receptors that are complementary to the specific antigen on the pathogen bind to the APC, this causes the T cell to be activated.

  Activated T cells divide by mitosis to produce clones.

  There are now many T cells in the blood, all of which have specific roles.
• What causes T cells to be activated?

  Binding to the complementary antigens (to their T cell receptors) on the surface of an APC.
• What is clonal expansion of T cells?

  Activated T cells divide by mitosis to produce clones.
• What 3 cells can be formed of clonal expansion of T cells?

  T helper cells

  T killer cells

  T regulatory cells
• What are T helper cells, their role?

  T helper cells are a type of white blood cell that release interleukins.

  Interleukins cause phagocyte activity to increase.

  Interleukins are needed to activate B cells, they bind to APCs along with B cells
• What is the role of T regulatory cells?

  T regulator cells down-regulate the host immune response by preventing T cells from attacking and killing uninfected host cells as well as shutting down the immune system once the body is cleared of the pathogen.

  Without checks, the immune system can spiral out of control and cause serious damage to the host.
• What are T memory cells?

  Memory cells remain in the blood, thus if the same antigen is encountered again the process of clonal selection will occur much more quickly.
• What is clonal selection?

  Process by which immune cells recognise and respond to specific antigens.
• How does T helper cells act to speed up the specific immune response?

  release cytokines/interleukins which stimulate clonal expansion of B cells
• What are the processes that lead to production of antibodies against an unfamiliar bacterium?

  B lymphocytes have antigen receptors on their surface complementary to only one antigen

  activated B cells divide by mitosis and differentiate into plasma cells

  the plasma cells secrete antibodies specific to the antigen
• Explain why different strains of bacterium produce immunologically distinct forms of the toxin, and how they will be dealt with by the immune system?

  toxins produced by each strain will be slightly different, each will have a different 3D shape

  the toxin acts as the antigen and the immune response is determined by the shape of the antigen

  antigen-presenting cells ingest the antigen and display the antigens on their surfaces

  T helper cells bind to the APC and produce interleukins

  B cells activated by T helper cells go through clonal expansion and clonal selection, b cells differentiate
• What would be symptoms of a lack of mature B lymphocytes in a person's blood?

  slower immune response/weakened immune system thus greater susceptibility to infection

  fewer plasma cells and thus fewer antibodies
• The specific immune response?

  When a pathogen enters the body it is recognised due to specific molecules on the surface of its cells called antigens.

  A phagocyte will engulf the pathogen and process these molecules by displaying them on the surface of the phagocyte.

  This cell will now interact with a T helper cell.

  The T helper cells produce interleukins that will activate the B lymphocytes.

  They start to divide by mitosis.

  These cells now differentiate into plasma cells, which synthesise and release antibodies.
• Why is the primary immune response slower than the secondary immune response?

  The primary response is slower due to clonal selection, expansion and the production of antibodies.

  The secondary response is faster as more antibodies are produced because of memory cells/ immunological memory.
• What is the function of a cytotoxic T cell?

  to produce perforin that causes pathogen-infected cells to lyse
• What is the role of a memory cell?

  to circulate the blood after an infection has been overcome
• What is the function of a T helper cell?

  to act as a co-ordinator of the immune response