Cytokine production plays a critical role in diseases caused by Kaposi's sarcoma–associated herpesvirus (KSHV). Here we show that a latent KSHV gene product, kaposin B, increases the expression of cytokines by blocking the degradation of their messenger RNAs (mRNAs). Cytokine transcripts are normally unstable because they contain AU-rich elements (AREs) in their 3′ noncoding regions that target them for degradation. Kaposin B reverses this instability by binding to and activating the kinase MK2, a target of the p38 mitogen-activated protein kinase signaling pathway and a known inhibitor of ARE-mRNA decay. These findings define an important mechanism linking latent KSHV infection to cytokine production, and also illustrate a distinctive mode by which viruses can selectively modulate mRNA turnover.