Clinical, functional, and immunologic effects of sublingual immunotherapy in birch pollinosis: A 3-year randomized controlled study

Background: Sublingual immunotherapy (SLIT) has been proved effective in allergic rhinitis, but there are few studies assessing its effects on inflammation and on the lower airways. Objective: We sought to evaluate at the same time the effects of SLIT on rhinitis symptoms, nasal inflammation, and lower airways function in patients with birch pollinosis. Methods: Adult patients with rhinitis and asthma monosensitized to birch were evaluated during a run-in pollen season and then randomized to receive openly either drugs alone or drugs plus SLIT and reevaluated in the subsequent 4 pollen seasons. Rhinitis symptoms and consumption of bronchodilators were assessed by means of diary card. A nasal smear for eosinophil count was carried out in and out of pollen seasons, and pulmonary function tests with methacholine challenge were performed at each season. Results: Of 79 enrolled patients, 27 dropped out, with a significantly higher rate of dropouts in the control group. There was a decrease in symptoms and bronchodilator use in the SLIT group versus the control group, becoming significant at the second and third pollen seasons, respectively (P < .01 at all times). Nasal eosinophils decreased significantly in the active group, starting from the third pollen season (P < .01). In the SLIT group a significant increase in FEV1, specific airways conductance, and maximal expiratory flow at 25% of forced vital capacity was seen starting from the second year and was associated with an increase in the methacholine threshold dose (P < .01). The differences were significant also at the intragroup comparison over time. Conclusion: SLIT achieved a significant clinical benefit in birch pollinosis, reduced the eosinophil infiltration in nasal mucosa, and significantly improved pulmonary function during the pollen seasons.