It is generally accepted that the early asthmatic response to inhaled allergen is a result of IgE-mediated mast cell activation. In contrast, the underlying mechanism of the late asthmatic response is much less clear.Objective
In order to investigate the pattern of mediator release during the early and late asthmatic responses to allergen, measurements of the urinary excretion of the mast cell markers 9α,11β-PGF2 and Nτ-methylhistamine were made. In addition, urinary levels of eosinophil protein X (EPX) and leukotriene E4 (LTE4) were measured.Methods
Twelve mild atopic asthmatics participated in the study. On the study day, pulmonary function was recorded at baseline and for 12 h after inhalation of allergen. Urine was collected prior to challenge and thereafter at 1 h intervals. Measurements of 9α,11β-PGF2 and LTE4 were made with enzyme-immunoassay, and levels of Nτ-methyl-histamine and EPX were analysed with radioimmunoassay.Results
All subjects developed both an early and late phase airway response. Within 1 h of the early peak airway response, there was a significant increase in the urinary concentrations (AUC/h) of 9α,11β-PGF2 (49.3 ± 9.2 to 142.5 ± 49.2; P < 0.001) Nτ-methylhistamine (10.4 ± 1.4 to 19.5 ± 1.4; P < 0.001) and LTE4 (43.7 ± 5.9 to 105.9 ± 21.3; P < 0.001). Levels of all three mediators were also significantly increased above baseline during the LAR to 79.4 ± 9.5 (P < 0.01), 19.8 ± 1.9 (P < 0.001) and 85.6 ± 10.4 (P < 0.001), respectively. Levels of EPX remained unchanged during the early and late responses (39.2 ± 10.2 to 37.5 ± 18.5, 33.9 ± 6.8).Conclusions
These results indicate that mast cell activation is a feature not only of the early but also the late asthmatic response. Finally, increased LTE4 supports the contribution of the leukotrienes to airway obstruction during both phases of the asthmatic response to allergen.