The presence of Dsg 3-reactive Th1 cells has been demonstrated in healthy carriers of PV-associated HLA class II alleles, and the Dsg 3-reactive Th1 clones derived from these individuals were restricted by HLA-DRβ1*0402 and DQβ1*0503 [146,151,153]. The gene discussed is HLA-DRB1; the disease is acquired polycythemia vera.