CD4 and infection: To get a detailed understanding of the expansion and functional differentiation of the responding lung CD4 Trm cells following infection we performed single-cell RNA-Seq (scRNAseq) analysis of TCRβ+ M2e-tetramer-binding FACS-sorted cells on days 3 and 8 post-infection, correlating with protection and decreased viral load (day 3 effector phase), and increased survival (day 8 recovery phase), respectively.