EFFICACY OF IMMUNOTHERAPY TO RAGWEED ANTIGEN TESTED BY CONTROLLED ANTIGEN EXPOSURE

Background: Immunotherapy is a recognized component in the management of allergic rhinitis. Its efficacy has been evaluated in a number of c linical field trials. These methods of evaluation are limited by contr ol of antigen exposure. Objective: A study was designed to evaluate th e efficacy of immunotherapy in ragweed-induced rhinoconjunctivitis usi ng an environmental exposure unit. Methods: Forty-three subjects were grouped into (1) immunotherapy group: ragweed-allergic subjects on mai ntenance ragweed immunotherapy for at least 2 years (N = 16), (2) posi tive control group: ragweed-allergic subjects who had never received i mmunotherapy (n = 16), and (3) negative control group: ragweed-nonalle rgic subjects (N = 11). Ragweed specific skin tests and ragweed IgE le vels were obtained prior to exposure. The study was done in a room whe re levels of 2,500 to 3,000 grains m(3) of ragweed were maintained ove r three hours. Symptoms were recorded every 15 minutes. Results: Nasal symptoms in the immunotherapy group were significantly less than in t he positive control group after 45 minutes (P = .025). Significant dif ferences were not observed for ocular symptoms. Combined nasal and ocu lar scores were 50% less in the immunotherapy group than in the positi ve control group by 75 minutes (P = .039). Ragweed-specific skin tests and IgE were significantly less in the immunotherapy group than in th e positive control group. Rhinoconjunctivitis symptoms in the negative control group were absent throughout. Conclusions: Controlled ragweed pollen exposure in this setting demonstrated that ragweed immunothera py significantly reduced symptoms of ragweed-allergic rhinitis but had no significant effect on ocular symptoms, This system presents opport unities for additional studies on immunotherapy for allergic respirato ry conditions.