Background Inhalation of hot, humid air (HHA: 37 °C, > 95% relative humidity (RH)) partially inhibits the early response to nasal challenge with antigen.
Objective To investigate whether HHA inhibited the late-phase response to nasal challenge with antigen and increased hyper-responsiveness of the nasal mucosa to histamine.
Methods Twenty subjects with seasonal allergic rhinitis, outside of their allergy season, participated in a randomized, 2-way cross-over study. The subjects continuously breathed room air (25 °C, 30% RH) or HHA delivered via a face mask during the entire experiment. Subjects were challenged intranasally with antigen 1 h after beginning conditioning. The response was monitored by symptoms and nasal lavage at 2-h intervals after the last antigen challenge. Eight hours after antigen challenge, nasal challenge with histamine was performed.
Results Exposure to HHA significantly increased nasal mucosal temperature from baseline without affecting nasal secretion osmolality. HHA significantly inhibited antigen-induced sneezes, congestion, pruritus, and human serum albumin levels during the early response to antigen challenge. HHA exposure, however, was associated with an 8-fold increase in the eosinophil influx and a 15-fold increase in the levels of eosinophil cationic protein during the late-phase response compared to room air. There were no significant differences in nasal hyper-responsiveness to histamine during either exposure.
Conclusion HHA partially decreases the early response to nasal challenge with antigen, but dramatically increases eosinophil influx. Increasing eosinophil number had no effects on the hyper-responsiveness to histamine. We speculate that the physical conditions of air differentially impact the stages of allergic inflammation.