CORONAVIRUS MHV-3-INDUCED APOPTOSIS IN MACROPHAGES

Infection with mouse hepatitis Virus strain 3 (MHV-3) results in letha l fulminant hepatic necrosis in fully susceptible BALB/c mice compared to the minimal disease observed in resistant strain A/J mice. Macroph ages play a central role in the pathogenesis of MHV-3-induced hepatiti s. in the present study we have shown that MHV-3 infection of macropha ges induces these cells to undergo apoptosis. Three methods to detect apoptosis were applied: flow cytometry analysis of nuclear DNA content , fluorescence microscopic visualization of apoptotic cells labeled by the TUNEL assay, and gel electrophoresis to detect DNA laddering. Apo ptosis in A/J and BALB/c macrophages was first detected at 8 h postinf ection (p.i.) and reached a maximum by 12 h p.i. The degree of MHV-3-i nduced apoptosis was much greater in A/J-derived macrophages than in B ALB/c-derived cells. Apoptosis was inversely correlated with the devel opment of typical MHV cytopathology, namely syncytia formation. Infect ed macrophages from A/J mice did not form synctia in contrast to the e xtensive synctia formation observed in BALB/c-derived macrophages. In MHV-3-infected BALB/c macrophage cultures, apoptotic cells were not in corporated into syncytia. Apoptosis was also inversely correlated with the expression of MHV-3-induced fgI2 prothrombinase in macrophages. T hese results add the murine coronavirus MHV-3 to the list of RNA-conta ining viruses capable of inducing apoptosis. (C) 1998 Academic Press.