To understand whether ligands for CYNK-expressed NK cell receptors are modulated by viral infection on target cells, we next established an in vitro infection model where a human lung epithelial cell line A549 is infected with IAV strain PR8/34 (H1N1) and analyzed the expression of NK cell activating receptor ligands on infected cells (Supplementary Figure 1). Here, KLRD1 is linked to viral infectious disease.