The IgE–mast cell pathway is a normal anti-parasite effector module. In allergy it is triggered by a harmless antigen, so the injury comes from misdirected targeting and disproportionate magnitude, not from a defective effector mechanism.
Where the error actually occurs
The error is upstream of the effector cell, in two decisions. First, during sensitization, the responding T cells commit to the Th2 program and drive IgE class switching. Second, the resulting antigen-specific IgE arms mast cells and basophils throughout the body. A mast cell that degranulates when its IgE is cross-linked is doing its job correctly; the misclassification happened before the antigen ever reached it.
Same module, different target
Helminth defense
- Antigen is a large extracellular parasite that cannot be phagocytosed
- IgE coats the parasite surface
- Mast cells and eosinophils bind IgE and degranulate onto the parasite
- Mediator release damages the parasite and is proportionate to a real threat
Allergy
- Antigen is a harmless protein or particle
- IgE coats the antigen and arms mast cells
- The same mast cells and eosinophils degranulate
- The same mediators damage host tissue, and the response is disproportionate to a non-threat
Because the defect is in antigen classification rather than in the effector pathway, the therapeutic logic is to shift the classification — for example by repeated antigen exposure that favors tolerance over Th2 commitment — rather than to repair the effector cells.