SERPINB5 and acquired polycythemia vera: Nevertheless, in line with our findings of SERPINB5 as a negative modulator of TGF-β activation, PV-IgG treatment in keratinocytes and PV patient skin biopsies showed reduced expression of SERPINB5, suggesting TGF-β activation in response to PV-IgG is at least in part regulated by SERPINB5.