FGF7 and infection: mRNA expression of Fgfr2b ligands in these four populations revealed that both Fgf7 and Fgf10 expression was significantly increased in the R4 fraction (CD31negCD45negEpCamnegSca-1high) compared to the other three major lineages of the lung (endothelial cells, epithelial cells, leukocytes), independent of IV infection (S3A Fig, right).