Background: Allergen-specific immunotherapy (SIT) is the only intervention for IgE-mediated respiratory disorders.

Objective: The aim of the study was to investigate the immunological modifications induced by SIT in patients allergic to olive and/or grass pollen by attempting to establish an association between these modifications and clinical improvements.

Methods: We studied 29 patients who were allergic to olive and/or grass pollen. Patients were randomized to 2 groups: an active treatment group, comprising 19 allergic patients who received SIT, and a control group, formed by 10 allergic patients who received pharmacological treatment for their allergic symptoms but not immunotherapy. We used flow cytometry to analyze intracellular expression of the cytokines IL-4, IFN-γ, IL-10, and TGF-β1 in CD4+ T cells, as well as expression of Foxp3, the costimulatory CTLA-4 molecule, and the non–costimulatory CD40L molecule. To assess clinical changes, patients recorded their medication consumption, symptoms, and the limitation of daily activities using diary cards and quality of life questionnaires.

Results: Six months after initiation of SIT, we recorded a reduction in cell surface CD40L expression in the CD4+ T-cell population and a shift in the cytokine production profile (decrease in IL-4–producing CD4+ T cells and increase in IFN-γ, IL-10, and TGF-β1). These changes persisted after 12 months. Simultaneously, a clinical improvement was observed.

Conclusions: SIT-induced clinical improvement is the result of immunological modifications such as a reduction in CD40L expression on CD4 cells and alteration in the cytokine production profile.

Key words: Pollen allergy. Immunotherapy. Cytokines. CD40-L. Foxp3.