Question

The lesions with itchy response showed improvement with antihistimines. What factors may caused mast cells to degranulate (this is not IgE response)?

Answer 1

Mast cell degranulation is a crucial event in IgE mediated hypersensitivity. The effector molecules released can be either primary or secondary mediators.

Primary mediators are synthesized and stored prior to mast cell activation. Examples include histamine,
eosinophil c hemotactic f actor (ECF), neutrophil c hemotactic f actor (NCF), and heparin.

Secondary mediators are either synthesized post activation of mast cells or result from breakdown of membrane phospholipids during degranulation of mast cell. Platelet- a ctivating f actor (PAF), leukotrienes, prostaglandins, bradykinins, several cytokines and chemokines are some of the examples.

Stimulation via IgE requires signalling through FcRI and FcRII receptors post crosslinking of receptor bound IgE with the allergen. However, other events might also cause ctivation and degranulation of mast cells which may act independently or synergistic to IgE signalling -

IgG

Complement components

TLR signalling

Cytokines and neuropeptides.

Specific factor for mast cell activation may vary with the kind of allergy.