Specific Defences

• Action of Lymphocytes

  1.Lymphocytes are white blood cells involved in the specific immune response.

  2. Lymphocytes respond to specific antigens on invading pathogens.

  3. Antigens are molecules present on the surface of cells

  4. Antigen binding leads to repeated lymphocyte division to form a clonal population.
• B Lymphocytes

  5 .B lymphocytes produce antibodies against antigens and this leads to the destruction of the pathogen.

  6. Antibodies are y- shaped proteins

  7. That have receptor binding sites specific to a particular antigen on the pathogen.

  8. Antibodies become bound to antigens, inactivating the pathogen

  9. The resulting antigen –antibody complex which can then be destroyed by phagocytosis

  10 They can respond to harmless antigens

  11 Leading to allergic reaction
• T – Lymphocytes

  12. T lymphocytes destroy infected body cells by recognising antigens of the pathogen on the cell membrane and inducing apoptosis.

  13. Apoptosis is programmed cell death.

  14. T lymphocytes attach on to infected cells and release proteins

  15. These proteins diffuse into the infected cells causing production of self-destructing enzymes which cause death.

  16. The remains of the cell are then removed by phagocytosis

  17.Failure of the regulation of the immune system leads to T lymphocytes responding to self- antigen7