Our data indicate that healthy controls that carry PV-associated HLA alleles exhibit a limited immunological activation similar to PV patients in terms of the pro-inflammatory cytokines IL-1α, IL-1β, IL-6, TNF-α, the Th2 cytokine IL-13, the Th17 cytokines IL-21 and IL-23, and the chemokine IL-8. The gene discussed is IL21; the disease is acquired polycythemia vera.