References: Iannello A, Tremblay C, Routy JP, Boulassel MR, Toma E, Ahmad A. Decreased levels of circulating IL-21 in HIV-infected AIDS patients: correlation with CD4+ T-cell counts. Viral Immunol. 2008 Sep;21(3):385-8. (RSG ELISA, serum, PubMed)
Volpe E, Servant N, Zollinger R, Bogiatzi SI, Hupé P, Barillot E, Soumelis V. A critical function for transforming growth factor-beta, interleukin 23 and proinflammatory cytokines in driving and modulating human T(H)-17 responses. Nat Immunol. 2008 Jun;9(6):650-7. (RSG ELISA, TC supernatant, PubMed)
Caprioli F, Sarra M, Caruso R, Stolfi C, Fina D, Sica G, MacDonald TT, Pallone F, Monteleone G. Autocrine regulation of IL-21 production in human T lymphocytes. J Immunol. 2008 Feb 1;180(3):1800-7. (RSG ELISA, TC supernatant, PubMed)