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

The induction of this activity temporally precedes induction by other stimuli, such as LPS or antigen-antibody complexes, as reported previously. At 2 h, although only 6% of total virally induced PCA is seen in the susceptible BALB/c strain, the quantity of PCA exceeds a maximum response by other agents, such as LPS. We have recently described (16) the kinetic characteristics and metabolic requirements for the induction of lymphoreticular PCA. We demonstrated, using LPS as a model stimulus, that lymphocyte triggering by this stimulus was a brief event, requiring only 5-10 min for detectable effect and 30 min for maximum triggering. Lymphocyte contact and induction of monocytes required 15 min for complete effect, but monocytes then required an additional 4 h for production of maximum PCA. In the viral induction of PCA, it appears there are differences in the kinetics of induction of PCA, with an initial response in just 1.5 h, although maximum PCA induction requires 12-16 h. This is not simply a matter of recruiting more monocytes or macrophages because we have demonstrated (14) in cytologic assays that virtually all monocytes/macrophages are recruited in the previously described responses. Thus, it is possible that different cellular mechanisms or products are operative for the induction of PCA by different stimuli.