Lessons in détente or know thy host: the immunomodulatory gene products of myxoma virus

The poxvirus, myxoma virus, encodes within its genome at least eleven different proteins that compromise, skew, or disable the innate and adaptive responses of its hosts. In the laboratory rabbit, Oryctolagus cuniculus, these effects result in myxomatosis, a fatal condition characterized by skin lesions and systemic immunosuppression. Interestingly, while myxoma infection also causes skin lesions in its natural host and in natural populations of O. cuniculus in Australia where this novel host and the virus have co-evolved, the condition of myxomatosis does not ensue and infection is not fatal. In this review I discuss the biochemical properties of the characterized immunomodulatory proteins of myxoma virus, and their pathogenic effects in laboratory rabbits. Disruption of any one myxoma immunomodulatory gene diminishes the severity of the infection without compromising infectivity. Thus, the characterized immunomodulatory genes appear not to be required for a productive infection in vivo. The differences in the severity of their effects in laboratory-bred versus wild O. cuniculus suggest that the outcome of myxoma infection is a consequence of the interplay between the viral immunomodulatory gene products and the cells and molecules of the host immune system.