IL21 and asthma: There are biomarkers useful for various phenotypes of non-eosinophilic and T2 low asthma; Th17 cells may be responsible for associated with a severe asthma phenotype, which is characterized by neutrophilic inflammation and interleukins such as IL-17A, IL-17F, IL-21 and IL-22 (Robinson et al., 2017).