lymphocytes

• What is humoral immunity

  • It involves antibodies
  • Antibodies are soluble in blood and tissue fluid
  • Old-fashioned word for body fluids is ‘humour’
  • There are over ten million types of B-cells and each make their own specific antibody that responds to a specific antigen.
• What is an antigen

  An antigen is any substance that when introduced into the blood or tissue induces an immune response. Most cells possess antigens in their cell surface membrane which act as markers enabling cells to recognise each other.
• what is antibody

  An antibody is a protein produced by B-lymphocytes in the presence of a specific, usually foreign, antigen.
• what do antibodies do

  A) phagocyte

  B) antibodies

  C) pathogens

  
• Humoral immune response

  B-cells synthesise antibodies that are specific protein molecules that can bind to foreign antigens.

  A) B lymphocytes

  B) plasma

  C) memory

  
• What happens in clonal selection

  1. When an antigen enters the blood or tissue fluid there will be one B cell that has an antibody on its surface whose shape is complementary to it.
  2. The B-cell binds to the antigen and together with substances released from helper T-cells, clonal expansion occurs.
  3. This produces many clones of the B-cell. Some of these clones are plasma cells which can produce the correct antibody. Some of the activated B-cells from memory cells.
  4. Plasma cells secrete loads of the antibodies specific to the antigen. These are called monoclonal antibodies.
• Memory cells

  • Responsible for secondary immune response
  • Live longer than plasma cells (often decades)
  • When they encounter antigen on a later date they undergo clonal expansion
• Plasma cells

  • Secrete antibodies in to blood plasma
  • Survive only for a few days
  • Make about 2000 antibodies per second
  • Responsible for immediate defence
  • Primary immune response
• Antigenic variation

  Antigenic variation refers to the mechanism by which an infectious

  agent such as a protozoan, bacterium or virus alters its surface proteins in order to avoid a host immune response.
• Label the diagram

  A) t lymphocyte

  B) effectors

  C) helpers

  D) memory

  
• role of t killer cells

  T killer or cytotoxic T lymphocytes cause lysis of the target cells.
• role of helper t cells

  Helper T cells release

  cytokines;

  • Stimulate B lymphocytes to initiate an antibody response
  • Stimulate phagocytosis by macrophages
  • Stimulate clonal expansion of B and T lymphocytes
• Role of memory cells

  Memory cells, remain dormant in the circulation until the host is next exposed to the same antigen.
• T lymphocytes self and non-self

  They can distinguish between self and non-self

  because:

  1. Phagocytes present the invaders antigens
  2. Body cells present antigens of invading virus
  3. Cancer cells have different antigens
  4. Transplanted cells have different antigens

  Cells that present foreign antigen are called Antigen

  Presenting Cells
• Cytotoxic T cells

  Kill Abnormal cells

  • Produce protein called perforin
  • Perforin makes holes in cell-surface membrane
  • This means the membrane becomes freely permeable to all substances
  • Dies as a result