Induction of monocyte procoagulant activity by murine hepatitis virus type 3 parallels disease susceptibility in mice

Virus. MHV-3 was obtained from the American Type Culture Collection, Rockville, Md. (ATTCC VR-262), and the lyophilized infected liver homogenate was reconstituted with 1 ml sterile phosphate-buffered saline (PBS), pH 7.4. The virus was plaque purified twice on monolayers of DBT cells. The virus was subsequently passaged once in DBT cells to prepare a seed stock. A working stock of virus was grown in 17 CL1 cells infected at a multiplicity of infection (MOI) of 10 -4 plaque-forming units (PFU)/eelI. This stock virus had a titer of 1.2 × 10 v PFU/ml and was used for all subsequent experiments. Virus was assayed on monolayers of L2 cells in a standard plaque assay, as previously described (31) (32) (33) (34) . Lethal dose--50% (LDso) was determined in BALB/c, C3H/St, and A/J mice and was calculated according to the method of Reed and Mueneh (35) , using an endpoint of 10 d.