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Science 19 June 2009:
Vol. 324. no. 5934, pp. 1525 - 1526
DOI: 10.1126/science.1176487
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Perspectives

Immunology:

A Chronic Need for IL-21

Lisa D. S. Johnson and Stephen C. Jameson

Chronic viral infections provoke a war of attrition between cytotoxic T cells (the CD8+ subclass) of the immune system and infected host cells. Although the CD8+ T cell response gradually whittles away at the viral load, the cells progressively become "exhausted" and lose function during a chronic infection (1). This exhaustion becomes more severe in the absence of helper CD4+ T cells, potentially leading to viral persistence and loss of virus-specific CD8+ T cells (1, 2). But how do CD4+ cells help? Three reports in this issue, by Elsaesser et al. on page 1569 (3), Yi et al. on page 1572 (4), and Fröhlich et al. on page 1576 (5), suggest an unexpected role for a specific cytokine produced by CD4+ T cells called interleukin-21 (IL-21) in controlling chronic viral infections.

Laboratory Medicine and Pathology, Center for Immunology, University of Minnesota, Minneapolis, MN 55455, USA.

E-mail: james024{at}umn.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)