Mast cells and asthma. The role of mast cell mediators in the pathogenesis of allergic asthma.

Upon a specific allergic reaction mediators released from mast cells found free in the bronchial lumen or in the epithelial surface loosen the interepithelial cell tight-junctions allowing the entrance of more allergen to deeper mast cells. The primary and secondary mediators thereby generated induce further increased vascular permeability which leads to the entrance of plasma proteins and platelets. The other immediate responses induced by mediator release are smooth muscle constriction, mucus secretion and leukocyte chemoattraction. Vagal afferent and reflex efferent stimulation are induced by histamine and probably other mediators which might contribute both to the bronchospasm as well as mucous gland secretion. Subacute responses include increased cellular infiltrates, mucosal edema, desquamation, basement membrane thickening, goblet cell hyperplasia and mucus secretion. These responses may occur because of the continued release of primary and secondary mediators as well as effects caused by the mast cell granule matrix-derived factors. It can thus be seen that many of the pathologic features of asthma may be attributed to mast cell degranulation.