Somnogenic effects of rabbit and recombinant human interferons in rabbits

Interferons (IFNs) are antiviral cytokines that possess several central nervous system activities. IFN therapy is associated with sleepiness, and the IFNs expressed during viral infection may be involved in the excess sleep associated with these infections. Most viruses stimulate the production of both IFN-alpha and IFN-beta. Although large doses of human IFN-alpha 2 are somnogenic in rabbits, the effects of species-specific IFNs on sleep in the rabbit have not been documented. We compared the somnogenic and antiviral effects of IFNs derived from rabbits to the effects of recombinant human (rh) IFN-alpha and IFN-beta. When injected intracerebroventricularly, rhIFN-alpha A/D, rabbit IFN-alpha/beta, and rabbit reference IFN induced non-rapid-eye-movement sleep and fever in a dose-dependent manner. However, the doses of rabbit IFNs required to induce sleep were much lower than those of human IFNs. Heat treatment of both rabbit IFNs and human IFNs greatly reduced their in vitro antiviral effects. The in vivo activities of rabbit IFNs and rhIFN-alpha A/D were significantly attenuated after heat treatment. However, rhIFN-beta retained its sleep-promoting action after heat treatment, suggesting that microbial contaminants were responsible for its somnogenic and pyrogenic activities. We conclude that IFN-alpha is somnogenic.