Currently, most of the protocols used for desensitization to Hymenoptera venoms consist of a very rapid increase in doses of venom extracts administered during the SIT in a day without systemic reaction of the patient which is not yet explained. The hypothesis is that this good tolerance is due to a rapid decrease in the response of mast cells and basophils to the allergen..

The main objective is to study basophil activation in response to the allergen during the first day of desensitization, measured by basophil activation test.

The initiation of desensitization follow a protocol of rapid growth rates. The basophil activation level in the course of desensitization will be analyzed by flow cytometry after in vitro stimulation by allergen.

Changes in T cell polarization is also analyzed by flow cytometry. Evolution of the expression of different proteins in blood basophils will be studied by measuring their messenger RNAs

Inclusion Criteria:

• Patients over 18 years and below 75 years age
• Patient who presented a generalized allergic reaction after an puncture of a hymenoptera
• Patient with positive skin tests against the venom of a hymenoptera
• Patient with positive specific IgE against the venom of a hymenoptera • to which an indication of accelerated desensitization was chosen in day hospitalization
• Information and consent signed by the patient
• Patient affiliated to french social security system
• For women of childbearing age, taking an effective contraceptive.

Exclusion Criteria:

• Patients with the following diseases: Mastocytosis, systemic infection or hospitalization within 4 weeks before inclusion, chronic inflammatory disease, cancer, unbalanced asthma, immune deficiency
• Patients on beta-blocker, following another specific immunotherapy, or ongoing immunosuppressive therapy.
• Pregnant or lactating
• People placed under judicial protection
• Patient participating or having participated in another biomedical research within six months