Depletion of circulating allergen-specific T(H2) T lymphocytes after allergen exposure in asthma

Background: In allergic asthma, CD4 ⁺ T lymphocytes are a fundamental component of local chronic inflammation. Their cytokine profile is oriented toward a T(H2) phenotype, characterized by production of IL-4, IL-5, IL-10, and IL-13. Egress of T cells from blood to airways after allergen challenge has been described. Objective: We have studied a cohort of six patients with asthma who had multiple allergies to investigate how exposure to allergen affects the proliferation of peripheral CD4 ⁺ T lymphocytes with different allergen specificities and lymphokine profiles. Methods: For each patient, CD4 ⁺ T-cell lines were generated by in vitro stimulation with sensitizing and with nonsensitizing allergens, and IL-4 and interferon-γ production by these lines was assessed. Proliferation of peripheral blood CD4 ⁺ T lymphocytes in response to the same allergens was measured before and 24 hours after inhalation challenge with a sensitizing allergen. Results: We found that each single sensitizing allergen can deplete peripheral blood of T(H2)-type CD4 ⁺ T lymphocytes specific for all sensitizing allergens, but not of T(H2)-type CD4 ⁺ T lymphocytes. Conclusions: Our results suggest the existence of mechanisms capable of sorting disease-associated antigen specificities together with defined lymphokine patterns into T lymphocytes that can migrate to target organs, in allergic asthma.