- Antigens are molecules ( proteins ) that can generate an immune respond.
- They are usually found on the surface of the cell.
- They can be used by the immune system to identify pathogens ( disease causing organisms), abnormal body cell ( cancer cells ) and foreign cells.
- They are like fingerprint of an organism and they are specific to each induvial.
- A phagocytes is a type of WBC that carries out phagocytosis ( engulfment of pathogens ).
- They are found in blood and in tissue.
- They recognise the foreign antigen on a pathogen .
- The cytoplasm of the phagocytes moves around the pathogen ( like arms ) engulfing it.
- The lysosome of the phagocytes produces lysozome ( digestive enzymes ) and breaks down the pathogen.
- The phagocytes then present the antigen on its surface triggering other immune system cells.
Phagocytes activate T-cells
- T-cell ( T-lymphocyte ) is another types of white blood cell.
- It has receptor proteins on its surface.
- They bind to antigens ( presented by phagocytes ) with complementary shapes to them.
- This activates the T-cells.
- Different T-cells respond in different ways.
- E.g helper T-cells releases chemical signals that activate and simulate more phagocytes and cytotoxic T-cells, which kill the foreign cells.
- T-cells also activate B-cells, which releases antibodies.
B-cells and Plasma cells
B-cells are also another type of WBC.
- It has a receptor protein on is surface that binds complementary antigens.to form an antigen-antibody complex.
- Each B-cell has a different antibody on its surface that only binds specific antigen. When they bind, the B-cells is activated.
- This process is called clonal sectional and B-cell divided into plasma cell.
- Plasma cells are identical to B-cells. They secret loads of (monoclonal) antibodies, specific to that antigen.
- An antibody has two binding sites, so it can bind to two antigens at the same type, clumping them together ( this is called agglutination)
- This make the job for phagocytes easier and more efficient.
Medical Diagnose test ( e.g pregnancy test )
- Pregnancy test detect the hormone hCG that is found in the urine of a pregnant women.
- The application area contains antibodies for hCG bound to coloured beads.
- When urine is applied to the application area, any hCG found will bind to the antibibody on the beads forming an antigen-antibody complex.
- Then urine is moved up the stick to the strip area carrying any beads with it.
- The test strip has immobilised hCG antibodies, is there is hCG present the test strip will turn blue, because the immobilised hCG antibodies bind to hCG.