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  • Created by: Nayo
  • Created on: 24-05-10 21:29

The Immune system

Foreign antigens trigger an immune response:

- Antigens are molecules (proteins or polysaccharides) found on surface of cells. When a pathogen invades body, antigens on cell surface as identified as foreign (activates cells in immune system.

- Four main stages involved in the immune response:

1. Phagocytes engulf Pathogens – type of white blood cell that carries out phagocytosis (engulfment of the pathogen). Found in blood and in tissues and first cells to respond to a pathogen inside the body:

· A phagocyte recognises the antigens on a pathogen.

· The cytoplasm of phagocyte moves round the pathogen (engulfing it)

· Pathogen is now contained in a phagocytic vacuole (a bubble) in cytoplasm of the phagocyte.

· Lysosome (organelle contains lysosomal enzymes) fuses with phagocytic vacuole. Lysosomal enzymes break down the pathogen.

· Phagocyte presents the pathogens antigens – sticks the antigen on its surface to activate other immune system cells.

2. Phagocytes activate T-cells

· T-cell another type of white blood cell. Has proteins on surface that bind to antigens presented to it by phagocytes. Activates the T-Cell.

· Different types of T-Cells respond in different ways:

- Some release substances to activate B-Cells.

- Some attach to antigens on pathogen and kill the cell.

3. T-cells activate B-cells, which divide into plasma cells

- B-cells type of white blood cell. Covered in anti-bodies which are proteins that bind antigens to form an antigen- antibody complex. Each b-cell has a different shaped antibody on its membrane – different


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