TPO and acquired polycythemia vera: We find that in the PV cohort there is a significant association between HLA type and anti-TPO antibody levels (p-value = 0.05): DRB1*0402−/DQB1*0503− (HLA-negative) patients (n = 33) have the highest prevalence of anti-TPO (A.R. 23.1%) followed by DRB1*0402+/DQB1*0503− patients (n = 117, A.R. 15.8%), DRB1*0402+/DQB1*0503+ patients (n = 19, A.R. 9.5%), and DRB1*0402−/DQB1*0503+ patients (n = 49, A.R. 4.8%) (Figure 5A), suggesting that the absence of DQB1*0503, regardless of the presence of DRB1*0402, predisposes patient to the development of anti-TPO antibodies.