Effects of pregnant mouse serum and pregnancy hormones on the replication in vitro of murine cytomegalovirus.

When mouse embryo fibroblasts cultivated in medium containing 2 per cent pregnant mouse serum were infected with mouse cytomegalovirus they gave 3-4 fold greater plaque counts and virus yield than when the medium contained 2 per cent normal mouse serum. Plaque size was increased up to two fold. There were similar differences between 2 per cent foetal calf serum and 2 per cent calf serum. When medium containing 2 per cent dialysed fetal calf serum was supplemented with physiological concentrations of oestrogen, progesterone and corticosteroid there was a 2-3 fold increase in plaque count and virus yield. The increase was only seen when the hormones were present both during virus adsorption and throughout virus replication. Any one of the hormones added by itself gave a smaller and more variable increase in yield and/or plaque count. Growth hormone by itself gave a 2 fold increase in virus yield; when added to the three other hormones it gave a 7-13 fold increase in virus yield but little change in plaque count. The three hormones also increased the rate of infection of resident peritoneal macrophages as scored by fluorescent antibody staining after a single cycle of virus growth in vitro. These experiments suggest that mouse cytomegalovirus infecting a pregnant mouse, or reactivating in a pregnant mouse would replicate more extensively.