Research Highlight A Little ‘Help ’ from IL-21 During Persistent Viral Infection

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. Despite decades of intense research, per-sistent viral infections still continue to out-smart investigators and maintain an active presence in the human population. Recent estimates suggest that 8–12 chronic infections can be found in each of us and comprise what is referred to as our ‘virome ’ (Virgin et al., 2009). For better or for worse, persistent viral infections do influence human physiology. At one end of the spectrum, persistent infections can heighten immune awareness, helping to ward off other pathogenic invader