ImmuneSystem

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.

 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.

4) Plasma cells make more antibodies to a specific antigen 

 They secrete loads of the antibody specific to the anitgen

Functions include:

• 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.

ANTIBODIES:

• protiens
• 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.