House dust mite subcutaneous immunotherapy does not induce new sensitization to tropomyosin: does it do the opposite?

BACKGROUND It is still uncertain whether house dust mite (HDM) tropomyosin present in allergen extracts can cross-sensitize patients receiving subcutaneous immunotherapy (SCIT) and thus induce food allergy. OBJECTIVES Our aim was to assess whether new sensitization to tropomyosin occurred during HDM-SCIT, and, if so, whether it was clinically relevant. PATIENTS AND METHODS The study sample comprised 56 HDM-allergic patients treated with SCIT using HDM extract. All patients were screened for specific IgE (sIgE) to mite tropomyosin (rDer p 10) before and after SCIT. In patients with a positive result, we also monitored the dynamics of sIgE to rDer p 10 and shrimp tropomyosin (rPen a 1) at several time points. The levels of sIgE were measured using the CAP System fluorescent-enzyme immunoassay. RESULTS sIgE to tropomyosin was found in only 5 patients, 3 of whom expressed low and clinically irrelevant levels of sIgE to Der p 10, while sIgE to Pen a 1 was not found. The remaining 2 patients expressed sIgE to both tropomyosins. In the first, the initial increase and subsequent decrease resembled the dynamics of the IgE antibodies usually seen in SCIT patients and were never accompanied by seafood-induced symptoms. In the other, a decrease in levels of sIgE to both tropomyosins resulted in the complete loss of his reactivity toward seafood. CONCLUSIONS Immunotherapy using HDM extracts does not induce clinically relevant sensitization to tropomyosin. In certain cases of combined mite and seafood allergy, treatment may even lead to the improvement of food allergy symptoms. The levels of sIgE to Der p 10 and Pen a 1 may be useful monitoring markers.