Poxviral modifiers of cytokine responses to infection.

Poxviruses include some of the most virulent of all human pathogens. In part, the virulence of these viruses stems from their abilities to counter host defenses against infection. A family of cytokine-response modifiers encoded by the poxviruses contribute to these countermeasures. The poxviral cytokine-response modifiers appear to affect cytokine responses in at least four different ways: (a) by inhibiting the synthesis and release of cytokines from infected cells; (b) by interfering with the interaction between a cytokine and its receptor; (c) by inhibiting cytokine signal transmission; and (d) by synthesizing virus-encoded cytokines that antagonize the effects of host cytokines mediating antiviral processes. Known poxviral, cytokine-response modifiers include CrmA, an inhibitor of the interleukin-1 beta converting enzyme; several secreted soluble receptors for tumor necrosis factor, interleukin-1, and interferon-gamma; and poxvirus-encoded growth factors resembling epidermal growth factor. Collectively, these and other as yet unidentified cytokine-response modifiers contribute to the inhibition of a variety of nonspecific and virus-specific immune defenses against virus infection. Information gained on the mechanisms used by poxviruses to modify cytokine-mediated processes should assist the development of novel therapies for a variety of diseases.