IL-17 mRNA in sputum of asthmatic patients: linking T cell driven inflammation and granulocytic influx?

Background: The role of Th2 cells ( producing interleukin ( IL-) 4, IL- 5 and IL- 13) in allergic asthma is well-defined. A distinct proinflammatory T cell lineage has recently been identified, called Th-17 cells, producing IL-17A, a cytokine that induces CXCL8 ( IL- 8) and recruits neutrophils. Neutrophilic infiltration in the airways is prominent in severe asthma exacerbations and may contribute to airway gland hypersecretion, bronchial hyper-reactivity and airway wall remodelling in asthma. Aim: to study the production of IL- 17 in asthmatic airways at the mRNA level, and to correlate this with IL- 8 mRNA, neutrophilic inflammation and asthma severity. Methods: We obtained airway cells by sputum induction from healthy individuals ( n = 15) and from asthmatic patients ( n = 39). Neutrophils were counted on cytospins and IL- 17A and IL- 8 mRNA expression was quantified by real-time RT-PCR ( n = 11 controls and 33 asthmatics). Results: Sputum IL- 17A and IL- 8 mRNA levels are significantly elevated in asthma patients compared to healthy controls. IL- 17 mRNA levels are significantly correlated with CD3 gamma mRNA levels in asthmatic patients and mRNA levels of IL- 17A and IL- 8 correlated with each other and with sputum neutrophil counts. High sputum IL- 8 and IL- 17A mRNA levels were also found in moderate-to-severe ( persistent) asthmatics on inhaled steroid treatment. Conclusion: The data suggest that Th17 cell infiltration in asthmatic airways links T cell activity with neutrophilic inflammation in asthma.