Cytokine Blocks Immune System's Cancer Defense

Researchers have uncovered the mechanism of immune evasion by which Kaposi's sarcoma-associated herpes virus (KSHV) avoids the body's immune response and promotes the development of cancer cells. Their findings were reported in the November 15, 2002, issue of Science.

The investigators, from the University of Pittsburgh Cancer Institute (PA, USA; www.pitt.edu), examined the expression of a virus-derived cytokine in KSHV. They found that this cytokine, viral IL-6 (vIL-6), not only inhibited immune function but also caused cancerous cells to grow. This comes about because during viral infection, host cells induce the antiviral factor interferon (IFN) to up-regulate the p21 gene, initiate cell cycle arrest, and inhibit virus replication but viral IL-6 blocks IFN signaling.

"The importance of this finding is that it demonstrates there is an overlap between the immune system and tumor suppressor pathways that are targeted by KSHV,” explained Dr. Patrick S. Moore, director of the molecular virology program at the University of Pittsburgh Cancer Institute. "It further demonstrates that viruses which inhibit immune functions also can, under some circumstances, induce tumor cells to grow because these viruses are attacking pathways that are important in both immunity and suppression of tumor growth.”




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