PCA for lung RNA-seq data. (A) Experimental schematic for mice used in RNA-seq. Naïve WT C57BL/6J were infected with X31 (H3N2) to generate memory mice; secondary infection was studied by infecting these memory mice with PR8 (H1N1), and primary infection controls were naïve WT C57BL6/J mice infected with PR8. (B) Top 10 enriched pathways from PC1 and PC2 as determined by GO. Statistical significance was calculated by the Wilcoxon rank-sum test.