Here we used a combination of cultured keratinocytes, established PV mouse models [6] and previously used biopsies from PV patients [23] to firstly investigate the occurrence of apoptosis and secondly, in the same PV models, caspase-3 activation and the consequences of caspase-3 inhibition in response to the Dsg3-specific pathogenic antibody AK23 [40] or purified PVIgG. The gene discussed is CASP3; the disease is acquired polycythemia vera.