[In vitro experiment on the rubella virus infection in the normal chorionic and decidual cells]

The mechanism of trans-placental Rubella virus (RV) infection was investigated in the in vitro system by using the normal human placental chorion and decidua. The standard RV strain (M-33) was inoculated in vitro by adsorption into the chorionic cells derived from the no RV infected normal pregnant women. 6 to 7 days later, these cells showed a relatively weak cytopathic effect (CPE) and released RV into the culture medium with a virological activity of 4 to 5 log10 FFU (focus forming unit)/0.1ml. Persistent RV infection was established in these cells following the gradual disappearance of CPE. The virological activity of RV from these carrier cells was in the range of 3 to 4 log10 FFU/0.1ml. By means of the indirect immunofluorescence technique, localization of specific RV fluorescence was observed on the cytoplasma of these cells. However no change was seen on the cellular growth rate or morphological appearance of these cells. Following the same process, neither CPE nor persistent infection was established on decidual cells from normal pregnant women. The present results seem to confirm the evidence we presented in the previous paper showing that the chorionic cells from RV infected pregnant women released RV into the medium and were considered to be the RV carrier. It might also be that the chorionic cells are highly susceptible to RV infection and, established easily, the process of the trans-placental RV infection is transmitted via the RV carrier state in the chorionic cells.