• allergn (dust,seafood) get into the body

• Immune system reacting by produce antibodies IgE

• It bind to basophils and surface of mast cell

• The person doesn't show symptoms yet at first

  
  

  Second exposure

• Allergen re-enter the body

• It bind to antibodies, and trigger driganulation

• It release chemical substances like histamine that cause swelling, itching,running nose etc.

• Leukotrienes and prostagladins cause inflammation and smooth muscle contraction

This may trigger an immune response that damages/destroys those cells.

• Localised redness

• blistering

• swelling

  ( can lead to inflammation )

Mechanism:

1. Antibodies (IgG/ IgM) combine with antigen forming, an immune complex.

2. Immune complex adheres to nearby cell.

3. Immune complex produce a c1 protein.

4. C1 protein splits into c5a and c3b.

   1. C5a attracts Neutrophils;

   2. C3b adhere to cell wall, marking where the Neutrophil should attack.

5. Neutrophils produce an enzyme, targeted at c3b.

6. The enzyme, cytotoxic granule breakdown the cells near c3b, triggering inflammatory reaction and tissue damage.

   1. If reaction happen to skin tissue, rashes will form.

Example:

Farmer's Lung

Farmer inhale spore from mouldy hay, antibodies treat the spore as antigen, cause type 3 allergic reaction.