Sublingual immunotherapy in Parietaria pollen-induced rhinitis: a double-blind study.

A double-blind, placebo-controlled study of immunotherapy was conducted in 31 patients with allergic rhinitis due to Parietaria pollen to evaluate the efficacy and safety of high doses of allergen via the sublingual route. The patients were assessed before and after a 10-month period of treatment by clinical (symptom-medication scores and specific nasal reactivity) and immunological (total IgE, specific IgE, IgG and IgG4 antibodies) parameters. High doses of Parietaria extract corresponding to a cumulative dose of 105 BU for each patient were administered with negligible side effects. The actively treated patients had significantly lower medication scores than those on placebo (p < 0.05) when the maximum pollen count was recorded, and at the end of the trial they showed a significant decrease in nasal reactivity (p < 0.02) and a significant increase in serum specific IgG4 (p = 0.02). No differences were detected in any of these parameters in the placebo group. Possible explanations for the mechanisms of sublingual immunotherapy are proposed.