Background Asthma, atopy and some forms of respiratory syncytial virus (RSV) disease are thought to be caused by T cells making IL-4 (Th2 cells). However, not all patients with similar patterns of clinical disease have the same underlying pathogenesis and the ability to detect immunopathogenic T cells by examination of the peripheral blood remains in doubt. With the prospect of specific immunotherapy for diseases caused by T cell subsets, it is important to determine whether peripheral blood mononuclear cell (PBMC) reactivity can be used to establish the presence of immunopathogenic responses and therefore to predict therapeutic effects.
Objective To detect IL-4 and IFN-γ production as markers of Th1 and Th2 responses in the peripheral blood of atopic and asthmatic adults.
Methods PBMC from 22 adult asthmatics (18 of whom were atopic) and 21 non-asthmatic volunteers (ten of whom were atopic) were stimulated with cat, birch and house dust mite allergens, human rhinovirus, RSV and recombinant chimaeric F/G protein from RSV in vitro. ELISPOT assays were used to enumerate cells producing IL-4 and IFN-γ.
Results Asthmatics had a sixfold increase in frequencies of IL-4-producing cells to cat and birch allergen (median values: 37 vs. 7 per million PBMC, P < 0.01 and 20 vs. 3 per million PBMC, P < 0.04, respectively) compared to non-asthmatics. By contrast, non-asthmatic atopics showed no specific increase in antigen-specific IL-4 responses and there was no evident correlation between skin prick test reactivity and ELISPOT results. Atopics had significantly more IFN- γ-producing cells specific for FG than nonatopics. while IFN-γ and IL-4 responses to other antigens were not significantly different.
Conclusion Enhanced IL-4 responses to non-viral aeroallergens are seen in adults with asthma, while enhanced IFN-γ responses to viral antigen FG were seen in atopics. In practical terms, ELISPOT assays for specific cytokines may provide a method that could be used to monitor antigen-specific T cell responses in peripheral blood.