IL21 and influenza: When we analysed the cytokine profile and other effector molecules expressed by lung-infiltrating γδ T cells by flow cytometry, we found the cells predominantly expressed IL-17A and barely other cytokines such as IL-10, IL-4, IL-6, IL21, and IFN-γ, indicating that IL-17A is a signature cytokine of lung γδ T cells upon influenza infection (Supplementary Fig. 1b).