The nasal response to histamine challenge: Effect of the pollen season and immunotherapy

To evaluate changes in the nasal response to histamine, we challenged 19 subjects with allergic rhinitis caused by ragweed (RW) before, during, and after the RW season with increasing doses of histamine diphosphate. We compared their response, as measured by symptoms and the levels of TAME-esterase activity and albumin recovered in the nasal lavage fluid, with response of two groups with allergic rhinitis undergoing immunotherapy with moderate-dose (N=16) and high-dose (N=11) RW (2 and 24 μg of antigen E [Amb a I] as maintenance dose, respectively). Four challenges with histamine were performed in each group: before, at the peak of, near the end of, and 2 weeks after the RW season. The three groups of subjects has similar skin sensitivity to antigen and levels of TAME-esterase activity and albumin recovered from nasal lavages after histamine challenge performed before seasonal exposure. Symptom diaries obtained throughout the season revealed a significant reduction only in the high-dose immunotherapy-treated group. At the peak of the season, the untreated group had more symptoms in response to the challenge compared with the challenges before and after the season (p=0.04 for both groups). The saline challenge occurring before challenging with histamine also demonstrated a significant increase at the peak of the season compared with increases before the season (p=0.02). This observation was also true for the levels of albumin and TAME-esterase activity. If the response after saline challenge was subtracted from each response after histamine challenge, no difference was found in the results between any of the visits. No changes occurred for the net albumin and TAME-esterase activity scores through the season. The saline challenges for the two immunotherapy-treated groups did not reveal a significant change, nor did the overall challenge vary during the season. We speculate that the increased responsiveness of the nasal mucosa during the allergen season may represent an increase in the baseline reactivity of the mucosa and not an increased responsiveness to histamine. Immunotherapy prevents this change in baseline reactivity.