Since a decreased level of serum IL-21, but increased expression of IL-21R on CD8+ T cells, was observed in the DLBCL samples, and due to the diverse correlations with disease progression, we hypothesized that a potential correlation existed between the serum level of IL-21 and the expression of IL-21R on the CD8+ T cells in the patients with DLBCL. The gene discussed is IL21; the disease is diffuse large B-cell lymphoma.