489 Does Sublingual Immunotherapy Work with an Immune Deviation Mechanism?

BACKGROUND: We aimed at finding out the immunological mechanisms of SLIT by studying the activity of IgE specific for the epitopes of Phleum in patients treated with SLIT for grass allergen and in a control group. METHODS: 30 patients allergic to grass were included in the study: 15 patients carried out a pre-seasonal SLIT for 2 years with the 5 grass mix extract from Stallergenes. 15 patients were not treated with SLIT. ELIGIBLE PATIENTS: Clear symptoms of seasonal rhinoconjunctivitis during the past year, positivity to Phleum skin prick tests (+++-) and specific IgE (3.5 kU/L). Prick tests were performed with extracts from Stallergenes; serum specific IgE for Phleum and rPhlp1, rPhlp2, rPhlp5, rPhlp6, rPhlp7, and rPhlp12 were determined through the Unicap system 100 IgE FEIA (Phadia Usala, Sweden). Wilkoxon and Fischer method were performed. Rast Inibition rpPhlp1/rpPhlp1, rpPhlp1/rpPhlp2 and rpPhlp1/rpPhlp4 were evaluated. RESULTS: IgE for rPhlp7 and rPhlp12 present only in some patients did not show significant modifications. Most patients treated with SLIT for 2 years, and all those showing improvement in symptoms, showed a less evident increase of specific IgE for rPhlp1 and rPhlp5 if compared with that of minor allergens, ie, rPhlp2, rPhlp4, rPhlp6. This difference was absent in control patients and in patients not showing clinical improvement. In patients showing clinical improvement the IgE ratio rPhlp5/rPhlp2 was significantly decreased (P = 0.02). A RAST inhibition study showed no cross-reactivity between rPhlp1/rPhlp2 and rPhlp1/rPhlp4. CONCLUSIONS: After 1 and 2 years of SLIT, the data show the following results: a significant increase of specific IgE for minor allergens and a less evident increase of specific IgE for major allergens in patients showing a clinical response to SLIT; a drastic decrease in IgE ratio for rPhlp5/rPhlp2. These results suggest that SLIT not only induces a TH2-TH1 isotypic switch, but also can act with a mechanism of immunological replacement. In fact, the production of specific IgE for minor allergens (rPhlp2, rPhlp4, rPhlp6) tends to replace the production of specific IgE for major allergens (rPhlp1, rPhlp5).