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Van der Veen RC, Dietlin TA, Pen L, Gray JD (1999) Nitric oxide inhibits the proliferation of Th1 and 2 lymphocytes without reduction in cytokine secretion. Cell Immunol 193: 194–201. PLoS ONE | www.plosone.org 9 November 2009 | Volume 4 | Issue 11 | e7863