IL13 and influenza: reported that PD-1 was upregulated on ILC2 progenitor cells and mature ILC2s in lungs after influenza infection and that blocking PD-1 on PD-1high ILC2s using anti-PD-1 antibody dramatically reduced cytokine (such as IL-13) production in the context of infection (27), indicating that PD-1 plays an indispensable role in ILC2 development and function.