Background: In asthma interleukin (IL)-13 is increased in the airway compared with non-asthmatic eosinophilic bronchitis. Whether this differential expression is specific to the airway or is more generalised is uncertain.

Methods: We sought to examine IL-13 expression in peripheral blood T-cells and eosinophils in asthma and non-asthmatic eosinophilic bronchitis. Peripheral blood CD3+ cell and eosinophil intracellular IL-13 expression from subjects with asthma, non-asthmatic eosinophilic bronchitis and healthy controls was assessed. The effect of priming by asthmatic serum on the release of IL-13 by peripheral blood mononuclear cells from healthy subjects was examined and the serum from these subjects was analysed for a range of chemokines and cytokines.

Results: The median (IQR)% intracellular IL-13 expression by CD3+ cells was increased in asthma [5.3 (2.7-9.8)%; n = 12] compared to non-asthmatic eosinophilic bronchitis [1.1 (0.5-3)%; n = 7] and healthy controls [1.7 (0.2-3%); n = 9] (p = 0.02), but was not significantly different in eosinophils across the groups. IL-13 released from healthy peripheral blood mononuclear cells (n = 10) was increased by asthmatic serum [117 (47.8-198)pg/ml] compared to control [78.5 (42.6-128)pg/ml; p = 0.02), but was not affected by non-asthmatic serum.

Conclusion: Our findings support the view that IL-13 expression is increased in peripheral blood-derived T cells in asthma and that asthmatic serum up-regulates IL-13 release from healthy peripheral blood mononuclear cells.