National Institute of Neurological Disorders and Stroke, The National Institutes of Health, Bethesda, MD 20892, USA *Correspondence to:Dorian B. McGavern, Tel: +1 301 443 7949; E-mail: mcgavernd@mail.nih.gov
Anti-viral CD4+ T cells are required to orchestrate and sustain the activities of the adaptive immune system during a persistent viral infection. Three recent studies suggest that CD4+ T cells accomplish this in part through the release of IL-21.
