Peripheral blood mononuclear cells  were acquired from 10 severe psoriasis patients and administrated by different concentrations of recombinant‐HMGB1 (rHMGB1) to detect the Th17 cell percentage, mRNA and protein levels of TLR4, IL‐23, IL‐17A and retinoid‐related orphan receptor γt (RORγt). The gene discussed is HMGB1; the disease is psoriasis.