Altered pathogenicity in the liver induced by a mouse hepatitis virus type 3 thermosensitive mutant.

Intraperitoneal inoculation into sensitive BALB/c mice of D85, a thermosensitive (ts) mutant, provokes acute hepatitis followed by recovery of the mice. The ts mutant was able to replicate in the liver. However, the maximal viral titre was obtained 2 days later than was the case with the wild-type (wt) MHV 3 infection; the viral antigens remained localized within small foci and no invasion of the entire liver was observed. The hepatocytes infected with D85 showed strong steatosis similar to that induced by wt virus, but the other lesions induced by MHV 3 (closing of endothelial cell fenestrae and hepatocytolysis) were not seen. An important feature noticed with the D85 mutant concerned the establishment, in the surviving animals, of persistent infection: this phenomenon was demonstrated by the decrease of viral titre in the liver, viral RNA detection, and the fact that viral antigens gradually decreased until the 3rd month post-infection.