Abstract
To study the pathogenicity of murine cytomegalovirus (MCMV) and to identify virulence determinants, we have isolated and phenotypically characterized a set of temperature-sensitive mutants. One mutant, PP269/38, was avirulent for 1-week-old BALB/c mice and restricted in its plaque formation and replication at 39 °C. Mutants PP242/68 and PP268/38 were 100-fold less virulent than salivary gland-grown virus (SGV), even after two passages in the salivary glands of 1-week-old mice. The former mutant was unable to replicate or form plaques at 39 °C whereas the latter replicated poorly at 39 °C but not at all at 40 °C although it was able to form plaques at 40 °C with a reduced plaque size. PP31/15 exhibited a 40-fold reduction in virulence compared to SGV after two passages in vivo and was unable to form plaques or to replicate at 40 °C; at 39 °C it was able to, with reduced efficiency. The remaining two mutants, PP99/3 and PP392/31, were 10-fold less virulent than SGV and were restricted at 40 °C. The six mutants have been classified into at least four complementation groups. These mutants may be useful for studying various aspects of MCMV pathogenicity.