IL-5 PRODUCTION BY ALLERGEN-STIMULATED T-CELLS FOLLOWING GRASS-POLLENIMMUNOTHERAPY FOR SEASONAL ALLERGIC RHINITIS

Grass pollen immunotherapy for the treatment of seasonal allergic rhin itis ('summer hayfever') results in improvement in symptoms, a reducti on in the early and late phase responses to allergen provocation and d ecreased tissue eosinophilia. Immunotherapy may act by altering the pa ttern of cytokine production by allergen-specific T cells from a 'Th2- type' (IL-4 and IL-5) profile to a 'Th1-type' (interferon-gamma (IFN-g amma)) profile, We set out to determine whether clinical improvement f ollowing specific allergen immunotherapy is accompanied by reduced pro duction of the pro-eosinophilic and archetypal 'Th2-type' cytokine, IL -5. Peripheral blood mononuclear cells (PBMC) were isolated from (i) 1 3 patients who had received 6 or 7 years' continuous conventional immu notherapy with timothy grass pollen (Phleum pratense): (ii) 14 patient s who had received 3 of 4 years of conventional immunotherapy followed by 3 years of placebo treatment; (iii) 12 matched seasonal rhinitic p atients who had never received immunotherapy; and (iv) 17 non-atopic n ormal controls. PBMC were stimulated with 20 mu g/ml and 200 mu g/ml P . pratense extract, or 10 mu g/ml of Mycobacterium tuberculosis purifi ed protein derivative (PPD) at 2 x 10(6) cells/ml and 5 x 10(6) cells/ ml. IL-5 concentrations in culture supernatants collected after 6 days ' culture were measured by ELISA. IL-5 production in response to stimu lation with P. pratense extract was highly reproducible and was elevat ed in both of the immunotherapy treated groups and the untreated rhini tics relative to non-atopic controls (P < 0.005 for each group relativ e to non-atopic controls, under each of the four conditions tested), H owever, no significant reduction was observed in IL-5 production when immunotherapy treated patients were compared with untreated rhinitic c ontrols, Moreover, abrogation of the cutaneous late-phase responses to allergen following treatment was not associated with reduced IL-5 pro duction by allergen-stimulated peripheral blood T cells. Reduced IL-5 production by peripheral blood T cells may not be necessary for immuno therapy to be effective. Local immunodulation of T cell responses may play a role in this form of treatment.