The immune system- Immune response step by step
Foreign Antigens trigger and Immune response
- Antigens are molecules( proteins or polysaccharides)
- found on the surface of cells
- when pathogen enters body the antigens identifies the cell as forgeign
- This activates cells in the immune system
Four stages of immune response :
1) Phagocytes (eg. macrophage) Engulf Pathogens-
- they are a type of white blood cell that carries out phagocytosis ( engulfing a pathogen)
- they are found in tissues and blood
- first cells to respond to pathogen inside the body
- First the phagocyte recognises the antigens on the pathogen as non self ( forgeign),
- then the cytoplasm of the pathogen moves round the pathogen; engulfing it.
- The pathogen is now in the phagocytic vacuole in the cytoplasm.
- A lysosome fuses with the phagocytic vacuole.
- The lysosomal enzymes break down the pathogen.
- The Phagocyte will then present the pathogens antigens on its surface to activate otherimmune system cells.
Second and Third stage
2) Phagocytes Activate T-cells
- Tcells are another type of white blood cell
- it has protiens that bind to the antigens presented to it by the phagocyte
- This activates the Tcell - ( some release substances to activate Bcells, Some attach antigens on a pathogen and kill the cell.)
3) Tcells activate B cells, which devide in to plasma cells
- Bcells are another white blood cell, that are covered in antibodies( that bind to antigens)
- then form antigen-antibody complex when they bind
- each B cell has a different shaped antibody
- When the antibody on the surface of a B-cell meets a complementary shaped antigen, it binds to it.
- This, as well as substances from Tcells activates the Bcell
- The activated Bcell divides in to plasma cells.
4th Stage and Antibody info
4) Plasma cells make more antibodies to a specific antigen
They secrete loads of the antibody specific to the anitgen
- Coating the pathogen to make it easier for a phagocyte to engulf it
- coating the pathogen to prevent it from entering host cells
- binding to and nuetralsing ( inactivating) toxins produced by the antigen.
- made of chains of amino acid monomers
- linked by peptide bonds
- the variable regions are what makes them specific ( due to amino acid sequence)
- complementry to a specfic antigen
- constant regions are all the same in all antibodies.