Allergen-specific T cells from birch-pollen-allergic patients and healthy controls differ in T helper 2 cytokine and in interleukin-10 production

Summary Background T helper (Th)2 cells play an important role in the development of IgE‐mediated diseases, with local overproduction of Th2 cytokines (IL‐4, IL‐5 and IL‐13) at the site of allergic inflammation. Furthermore, IL‐10 has been suggested to play a modulatory role in the induction and maintenance of allergen‐specific tolerance in human atopic diseases. Aim We studied whether circulating allergen‐specific Th2 cells persist outside the season of exposure in patients mono‐sensitized to birch pollen and whether healthy control individuals also have allergen‐specific Th2 cells. We also studied whether IL‐10‐producing allergen‐specific T cells can be found in circulation either in healthy controls or in allergic patients. Methods Blood was drawn outside the birch‐pollen season from 15 birch‐pollen‐allergic patients, with seasonal respiratory symptoms and with (n=12) or without (n=3) oral allergy syndrome, and from 10 matched healthy controls. Peripheral blood mononuclear cells (PBMCs) were stimulated in vitro with recombinant Bet v 1 allergen, control antigen tetanus toxoid (TT) and anti‐CD3/CD80. In part of the cultures, rIL‐4 was added in order to reinforce the allergen‐specific Th2 cell responses. Results In the presence of rBet v 1, T cells from allergic patients, but not from healthy controls, produced IL‐4, IL‐5 and IL‐13. IL‐5 production by patients' T cells was further enhanced by adding more IL‐4. In contrast, rBet v 1 together with IL‐4‐induced significant IL‐10 production in control subjects but not in patients. Both Th1 and Th2 cytokines were equally induced by polyclonal stimulation in allergic patients and controls, but in the presence of IL‐4, polyclonally induced IL‐10 production was lower in the patient group. Conclusion rBet v 1‐specific Th2 cells circulate outside the season of exposure in the blood of birch‐pollen‐allergic subjects but not in healthy controls. Allergen‐specific T cells were also demonstrated in controls but these cells produce IL‐10 when stimulated with rBet v 1 in the presence of IL‐4. Our data reveal a different allergen‐induced cytokine profile in birch‐pollen‐allergic patients vs. controls, and suggest that a regulatory mechanism involving IL‐4‐induced allergen‐specific IL‐10 production might be defective in allergic subjects.