IGHE and papilloma: Although Igh7–/– mice showed an equivalent level of DNA-damage to WT following carcinogen exposure (Figure 3—figure supplement 1a), as assessed by staining for the phosphorylated histone H2A variant H2AX (γH2AX), only a few Igh7–/– mice developed tumours and the ones that did grew only very few and significantly smaller papillomas (Figure 3a), suggesting that the lack of IgE during TPA promotion hindered tumour growth.