Patients who will be enrolled in this study are allergic patients from the Immuno-Allergology department of the CHL, who will anyway undergo routine antigen-specific immunotherapy for medical reasons. These immunotherapeutic protocols are already established and used by experienced specialists at the CHL and will not be modified for the purpose of this research project. If patients eligible for AIT agree to participate in our research project, the investigators will collect blood and stool samples during the course of treatment. Depending on the allergy to be treated, there are two routine desensitization protocols: an ultra-rush protocol is performed for insect sting desensitization, while a conventional protocol is used for pollen desensitization.