The observations on development of new sensitizations induced by specific immunotherapy are contrasting. Studies demonstrating new IgE reactivities to allergenic components in pollen extracts administered with SLIT did not report association with clinical symptoms [6, 7]. Concerning dust mite immunotherapy, the relevant allergen is tropomyosin, occurring in mites, crustacean and molluscs and in a number of other invertebrates [10–13]. A first study found that SCIT with dust mite extract induced an increase of IgE response to snail or shrimp and the occurrence of clinical symptoms following their ingestion . However, only in two patients, who were negative at baseline to tropomyosin, a new sensitization actually took place. There are reports that subjects already clinically allergic to foods containing tropomyosin may worsen their food allergy symptoms following mite immunotherapy [14, 15], but this is a different issue. Indeed, in a study on two groups of children, respectively treated or not by mite immunotherapy for a mean duration of 19 months, the only new sensitization to snail was found among children not treated with immunotherapy . Of course, the eating habit is an important factor: in the study by Meglio et al less than 20% of children had previously eaten snails , but in the study by Asero et al all the included patients ate crustaceans and molluscs of any kind with no clinical reaction . It is also true that a sensitisation to shrimp's tropomyosin can be found in subjects allergic to mites who never ate shrimps or shellfish .
We studied patients living in a geographic area in the province of Cuneo in northwest Italy, where molluscs are widely consumed as part of the local gastronomic tradition. There are two small cities specifically within the area, Borgo San Dalmazzo and Cherasco, where the consumption of snails in particular is quite high; snails are even the subject of frequent local culinary festivals. All patients had a personal histories free from systemic allergic reactions to crustaceans and molluscs (oysters, snails, prawns, lobster etc.). The main finding of our study is that all 134 patients with negative rPen a1 IgE before starting immunotherapy, remained tropomyosin IgE negative after completing the mite immunotherapy course. Of course, an assessment of Der p 10-specific IgE would have been more specific, but such reagent was not available at the time of the study. In addition, the shrimp skin test and shrimp-specific IgE assay proved positive in shrimp-allergic patients, so that the reliability of those tests in detecting positive subjects is reasonably ascertained.
To our knowledge the present paper is the first one in which the evaluation of a large number of patients treated with mite sublingual/oral vaccines did not result in a neo-sensitisation to tropomyosin, which was significantly present (as mite group 10) in the extract administered. This suggests that a persistent and continuative ingestion of a tropomyosin source as mite extract might not be enough to neo-sensitize mite allergic patients. The length of time a given subject receives SLIT seems also be a notable factor. The patients we studied had their treatment for a mean duration of more than 2 years, that may be considered a reasonable period in which a neo-sensitisation can occur. Although the occurrence of IgE reactivity to tropomyosin was reported in initial observations on patients treated with mite SCIT , a subsequent study specifically addressing the issue was unable to observe such phenomenon within a 3-year duration of mite SCIT . Our findings demonstrate that also with prolonged SLIT neo-sensitisation to tropomyosin does not occur, and this was confirmed by negative skin tests to shrimp extract performed in all treated patients.
Obviously, the possibility of a neo-sensitisation to tropomyosin during SCIT or SLIT cannot be completely excluded. However, it is possible that occurrence of side effects induced by crustaceans or molluscs ingestion during mite immunotherapy could be due to lack of information about a pre-existent state of sensitisation to tropomyosin in these patients. To avoid possible allergic reactions to tropomyosin containing foods, we believe that assessment of a pre-existing sensitisation to tropomyosin by skin test and specific IgE measurement should be performed prior to start mite extract immunotherapy.