IMCs enhance papilloma formation. (A) Papilloma development in Tg.AC and S100A9Tg;Tg.AC bitransgenic mice after TPA treatment for 6 wk. Each group included seven mice. Two-way ANOVA, P = 0.0071. (B) Papilloma development in lethally irradiated Tg.AC mice that received BM from S100A9Tg or WT (control) mice. TPA treatment started 3 wk after the BM transfer. Each group included four mice. Two-way ANOVA, P = 0.035. (C) Papilloma development in S100A9Tg;Tg.AC mice treated with Gr-1 antibody and TPA as indicated in the graph. Each group included five mice. Two-way ANOVA, P < 0.001. (A and C) Mean and SD of the number of papillomas per mouse are shown. (D) Proliferation of keratinocytes in WT and S100A9Tg FVB/n mice treated for 5 wk with TPA. The proportion of proliferating Ki67⁺ cells among all cytokeratin 14⁺ keratinocytes was calculated in at least 100 cells. Each group included three mice. *, P < 0.05 between TPA- and acetone-treated WT mice; ##, P < 0.01 between TPA-treated WT and S100A9Tg mice. (B and D) Mean and SD are shown.