Background: Human cytomegalovirus (hCMV) infection of the trophoblasts is a crucial event in virus transmission from mother to child, being one responsible factor for intrauterine infection of the unborn. Differences of virus replication in trophoblasts depending on time point of pregnancy and degree of differentiation of trophoblasts might influence this transmission. Furthermore, immunological reactions of the trophoblasts to hCMV infection might be important defence mechanisms too.
Objectives: hCMV replication and interleukin-6 release in trophoblasts and trophoblast like cells (choriocarcinoma cells) was investigated.
Study design: Trophoblasts from term and 1st trimester placentas were isolated and infected with hCMV. hCMV production and release to the supernatant as well as interleukin-6 release and interleukin-6 mRNA production by these infected cells was measured. Choriocarcinoma cell lines (JEG-3, JAR) were treated the same. Non-infected trophoblasts were used as controls.
Results: In 1st trimester trophoblast, term trophoblasts and JEG-3 permissive hCMV replication was observed, although with different kinetics and efficiency. In JAR no complete virus replication was seen. High levels of interleukin-6 were measured in the supernatants of all hCMV infected cells immediately after infection. IL-6 mRNA upregulation was seen 48 h after infection in those cell types replication of hCMV occurred (1st trimester trophoblasts, term trophoblasts, JEG-3). At that time-point hCMV immediate early proteins appeared. In JARs no virus production and no IL-6 mRNA upregulation was seen, and IL-6 levels in the supernatant of these hCMV infected cells declined significantly until day 6 after infection compared to mock infected cells.
Conclusion: These observations show that hCMV replication is influenced by the degree of trophoblast differentiation. Interleukin-6 is upregulated by hCMV infection, but is independent of complete virus replication.