Cell mediated immunity

• What is an antigen?

  A substance that is recognised as foreign by the immune system and produces an immune response.
• T lymphocytes: a type of lymphocyte that is associated with cell mediated immunity
• Cell-mediated immunity: immunity involving body cells
• Response of T lymphocytes to pathogens:

  • This uses the antigen-presenting cell from phagocytosis by macrophages
  • Receptors on specific T helper (Th) cells fit exactly onto these antigens
  • This attachment activates the Th cell to divide rapidly by mitosis and form a clone of genetically identical cells
  • The cloned T cells can develop into memory cells, stimulate phagocytes to carry out phagocytosis, stimulate B cells, or activate cytotoxic T cells (Tc cells)
• How do cytotoxic T cells kill infected cells?

  By releasing a protien called perforin that makes holes in the cell membrane. This makes it permeable to substances and the cell dies as a result