TNF and acquired polycythemia vera: ST18, a regulator of apoptosis and inflammation overexpressed in the skin of PV patients compared to healthy individuals, has been hypothesized to have a role in the pathogenesis of pemphigus provoking an elevated production of TNF-α, IL-1α, and IL-6 and favoring a PV IgG-induced cell–cell altered adhesion (162) Although in Egyptian, Jewish, and Iranian populations SNPs of ST18 and PV association was reported, in Italian (163), Chinese and German population no linkage between ST18 SNPs and PV was demonstrated (161, 164, 165).