Th17 cells are now commonly thought to be important in the control of several chronic immunological disorders, including asthma and chronic obstructive pulmonary disease. The current understanding of the function of Th17 cells in the development of various asthma phenotypes and chronic obstructive pulmonary disease is discussed in this study. Recently, it was shown that Th17 cells, as well as a novel population of Th17/Th2 cells, accumulate in the bronchoalveolar lavage fluid of asthmatic patients and are positively associated with airway obstruction and steroid resistance. These individuals frequently have severe steroid-resistant asthma and bronchial neutrophilic inflammation.

IL-17 targeted treatments may be beneficial in severe steroid-resistant asthma with predominant bronchial neutrophilic inflammation. According to this viewpoint, defining clinical phenotypes and inflammatory endotypes of asthma in each patient is essential for customizing the treatment strategy.