37. Allergic reaction
Main article: Allergy
Mast cells
The main mediators of allergic reactions are the mast cells, but basophils are also involved. They are activated when IgE bound to their surface FcεRI and this IgE subsequently binds to an antigen. This causes the activation of two protein tyrosine kinases in the cell, Lyn and Syk, which transmit the signal into the cell, causing the mast cell to release the molecules that mediates the allergic reaction.
The molecules released by mast cells and basophils must be divided into two categories: the ones that are stored in the cell and released when the signal arrives, and the ones that are produced and released when the signal arrives.
Preformed molecules
The preformed molecules are summarized in the table below.
| Name | Function |
|---|---|
| Histamine | Vasoactive amine |
| Tryptase, chymase | Proteases |
| Hexoseaminidase | Acid hydrolases |
| Heparin | Unknown (not anti-coagulation) |
| Adenosine | Bronchoconstriction, anti-coagulation |
Newly formed molecules
The newly formed molecules are the inflammatory cytokines like TNFα and IL-6, but more importantly the arachidonic acid derivatives, the eicosanoids. The eicosanoids are the prostaglandins and leukotrienes, which are formed from cyclooxygenase and lipoxygenase, respectively.