Airway neutrophils and interleukin-17.

It is well known that exacerbations of obstructive airways disease such as asthma and chronic obstructive pulmonary disease are associated with an increased number of neutrophils in the airways. However, the mechanisms behind this phenomenon are poorly understood. There is in vivo experimental evidence that the number of airway neutrophils is controlled by certain T-lymphocytes, but the mediators responsible for this lymphocyte-related neutrophilia have not yet been identified. In this review, novel evidence that the T-lymphocyte-related cytokine interleukin (IL)-17 can link the activation of certain T-lymphocytes to the recruitment and activation of airway neutrophils is described. The IL-17-induced neutrophil recruitment is mediated via induced CXC chemokine release through steroid-sensitive mechanisms and is modulated by release of endogenous tachykinins. These effects of IL-17 are potentiated by other pro-inflammatory cytokines such as (IL-1beta) and tumour necrosis factor-alpha. Clinical studies are needed to evaluate whether or not targeting these mechanisms can provide a useful pharmacotherapeutical approach against exaggerated mobilization of neutrophils in obstructive airways disease.