Interleukin-17 cytokine signalling in patients with asthma

Asthma remains a global health problem and, therefore, more effective pharmacotherapy is needed. This is particularly true for chronic and severe asthma. In these clinical phenotypes, chronic inflammation involving neutrophils is likely to play a pathogenic role, making it interesting to target cytokine signalling involved in the accumulation of neutrophils. Therefore, it is of interest that the archetype T-helper 17 cell cytokine interleukin (IL)-17A, perhaps also IL-17F, controls neutrophil accumulation, mucus secretion, macrophage mobilisation and smooth muscle reactivity in various experimental airway models. However, much less is known about the involvement of signalling via IL-17 cytokines in humans with asthma. Existing evidence suggests that these cytokines are released from several types of immune cells in asthma and, for IL-17A, there is a local increase associated with disease severity, with the mobilisation of neutrophils and smooth muscle cells locally in the airways. Even though the causative role of IL-17 cytokines remains unclear, there is potential for clinical utility in targeting IL-17A specifically in patients with moderate-to-severe asthma and high reversibility. There is a need for new and well-powered clinical investigations of signalling via IL-17 cytokines in this clinical phenotype.