Figure 1.

Development of an early- and late-phase airway response in response to allergen in a sensitized individual. The early phase fall in lung function is due to mast cell-dependent bronchospasm, mediated largely by leukotrienes. The late-phase response is mediated by activated Th2 cells and suppressed by drugs that inhibit T-cell function such as steroids and cyclosporine. It is proposed that CRTH2 is involved in both mast cell-mediated activation of Th2 cells and the amplification of Th2 recruitment that occurs as a result of IgE-facilitated antigen presentation by airway dendritic cells.