Immune system

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Antigens

- 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.

(http://static.squarespace.com/static/512942dce4b01fa6748b1794/t/529bf275e4b080ab7c0213e2/1385951862611/antigens.jpg)

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phagocytes

- 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.

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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.

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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.

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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.

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