Nasal AMP and histamine challenge within and outside the pollen season in patients with seasonal allergic rhinitis

Background: Nasal hyperreactivity is a prominent feature of allergic rhinitis. Variation in nasal hyperreactivity with different challenge agents in and out of the pollen season has not been examined.Objective: We sought to compare nasal hyperreactivity with different challenge agents before, during, and after the pollen season.Methods: Grass pollen-monosensitized patients performed cumulative-dose challenges with nasal AMP (25-800 mg . mL(-1)) and histamine (0.25-8 mg . mL(-1)) before, during, and after the grass pollen season. Outcomes included the provocative concentration of agent causing a 30% decrease in the peak nasal inspiratory flow (PNIF) (PC30), recovery profile, and diary cards.Results: Nineteen participants completed per protocol. AMP PC30 values for PNIF worsened by 1.33 (95% CI, 0.20-2.44; P = .02) doubling dilutions during the season but recovered after the season. The AMP recovery curve showed a 214.39% difference (95% CI, -21.11% to -7.66%; P < .001) during the season and remained abnormal after the season (-8.05% [95% CI, -14.78% to -1.33%; P <.05). Histamine PC30 values did not change during the season, but recovery was prolonged by 214.47% (95% CI, 222.19% to -6.76%, P < .001), returning to baseline values after the season. Nasal symptoms, domiciliary PNIF, and serum eosinophil-derived neurotoxin levels returned to baseline values after the season.Conclusions: There is a reduction in AMP PC threshold but not histamine PC threshold during the pollen season, indicating that AMP is a more sensitive indicator of allergic inflammation. The residual hyperreactivity to nasal AMP, but not histamine, outside of the pollen season, seen as a persistently prolonged recovery curve, suggests the presence of primed airway mucosal mast cells, even in asymptomatic patients, and persistent activation of mediator pathways, such as cysteinyl leukotrienes. (J Allergy Clin Immunol 2011;127:173-8.)