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…