ATTENUATION OF B5R MUTANTS OF RABBITPOX VIRUS IN-VIVO IS RELATED TO IMPAIRED GROWTH AND NOT AN ENHANCED HOST INFLAMMATORY RESPONSE

The rabbitpox virus (RPV) B5R protein, synthesized late in infection, is found as a 45-kDa membrane-associated protein of the envelope of in fectious extracellular enveloped virus (EEV) and as a 38-kDa protein s ecreted from the cell by a process independent of morphogenesis. The p rotein is not found associated with intracellular mature virus (IMV). Deletion of the gene attenuates the virus (RPV Delta B5R) in animals ( mice and rabbits), has relatively little effect on formation of IMV, p revents EEV formation in some but not all cells, and leads to a reduce d host range. Analysis of the sequence of the protein suggests related ness to factor H of the complement cascade. Collectively, these observ ations suggest that attenuation of the virus in vivo could be linked t o an inhibition of the inflammatory response, a deficiency in growth, or both, In this report we have analyzed the behavior of RPV Delta B5R in infected mice and rabbits and conclude that attenuation of the mut ant virus likely results from simple failure to grow within the infect ed animal and that the inflammatory response probably contributes litt le to the observed attenuation. (C) 1997 academic Press.