a, Principle component analysis (PCA) of gene-expression profiles obtained from MmuPV1-induced warts (n = 4; blue triangles), MmuPV1-infected skin (n = 4; pink squares) or sham-infected skin (n = 4; grey circles), and MmuPV1-infected tumours (n = 4; red squares) or sham-infected tumours (n = 4; black circles) of SKH-1 mice. Note that DMBA–UV-induced skin tumours from MmuPV1-infected mice are indistinguishable from skin tumours from sham-infected mice, whereas both have very distinct transcriptional profiles compared with MmuPV1-driven warts. b, c, Volcano plots of differentially expressed genes in MmuPV1- versus sham-infected skin (b; n = 4 per group), and skin tumours and warts (n = 12) versus MmuPV1- and sham-infected skin (c; n = 8). Gm5416 is also known as Csta3. P values were calculated using the DESeq2 R package (v.2 1.6.3), and the resulting P values were adjusted using the Benjamini–Hochberg method for controlling the false discovery rate. The 20 genes that were upregulated in skin tumours and warts compared with MmuPV1- and sham-infected skin are shown in the table on the left. d–f, Analysis of the expression of immune genes in human skin lesions on the basis of the mouse RNA-seq data. d, Representative macroscopic and H&E-stained histological images of SCC, wart, seborrheic keratosis (SK) and unaffected human skin. Scale bar, 500 μm. e, Relative gene expression in SCCs (n = 7) and warts (n = 5) compared with normal skin (n = 8). f, Normalized relative gene expression in SCCs (n = 7), warts (n = 5) and seborrheic keratosis (n = 5) compared for several DAMP genes. Average relative gene expression in the normal skin was used for normalization. GAPDH is used as the reference gene. Two-tailed Mann–Whitney U test; *P < 0.05, **P < 0.01, NS, not significant; data are mean + s.d. (e, f).