Role for cysteinyl leukotrienes in allergen-induced change in circulating dendritic cell number in asthma

Dendritic cells are important antigen-presenting cells. After an allergen inhalation, their numbers rapidly decrease in circulation and increase in the airway mucosa. To investigate whether allergen-induced changes in the number of circulating dendritic cells are mediated by cysteinyl leukotrienes. In a randomized, double-blind, crossover study, we examined the effects of 2 weeks of treatment with pranlukast (a cysteinyl leukotriene 1 [CysLT1] receptor antagonist) 300 mg twice daily and placebo on allergen-induced changes in airway responses and circulating dendritic cells in 15 subjects with mild asthma. We examined by flow cytometry, before and at 3 hours and 24 hours after allergen inhalation, the proportion of myeloid (CD33+) and plasmacytoid (CD123+) dendritic cells (HLA-DR+, CD14–, CD16–) among all peripheral blood mononuclear cells. The fraction of dendritic cells expressing CysLT1 receptor was also determined. Compared with placebo, pranlukast significantly attenuated both the maximum early (by 55%) and the late (by 39%) asthma responses, the allergen-induced methacholine airway hyperresponsiveness, and the increase in macrophage inflammatory protein 1α and 3α in induced sputum. A significantly greater proportion of CD33+ cells (55%) expressed CysLT1 receptor compared with CD123+ cells (11%). Consistent with this, pranlukast prevented the allergen-induced decrease in CD33+ dendritic cells at 3 hours postallergen (mean Δ from baseline, +4.4%) compared with placebo (mean Δ, −8.4; P < .05), but not CD123+ cells. Pretreatment with pranlukast attenuated allergen-induced airway responses and the decrease in circulating myeloid dendritic cells, demonstrating a novel role of cysteinyl leukotrienes in dendritic cell trafficking.