ABSTRACT
Within 12 hours of contact with antigen, a late-phase reaction occurs (Fig. 33.3). Arachidonic acid metabolism in the mast cell generates prostaglandins and leukotrienes, which further increase blood flow and vascular permeability (Fig. 33.4). Cytokines such as interleukin-3 (IL-3), IL-4, IL-5, and tumor necrosis factor-a (TNF-a) are produced by both activated mast cells and helper T cells, and these further prolong the allergic reaction. The mediators and cytokines released by mast cells and helper T cells cause an influx of monocytes, more T cells, and eosinophils into the site of allergen entry. The late-phase reaction is dominated by this cellular infiltrate. The cells of the infiltrate, particularly the eosinophils, make a variety of products that are thought to be responsible for much of the tissue damage and overproduction of mucus that is associated with chronic allergic reactions. Mast cells are also reactivated and thus the inflammatory reaction is perpetuated. Cytokineproducing NK T cells have also been implicated in allergic asthma.
