Highly sensitive detection and localization of maternally acquired human cytomegalovirus in placental tissue by in situ polymerase chain reaction.

BACKGROUND Transplacental transmission of human cytomegalovirus (CMV) can result in congenital malformations, although details on the mechanisms of transmission and the location of CMV in infected placentae need to be described.METHODS. Placental tissue from term (third trimester) deliveries was screened for CMV infection by polymerase chain reaction (PCR), in situ PCR (IS-PCR), and IS reverse-transcriptase PCR (IS RT-PCR).RESULTS. CMV DNA was detected in tissue samples from 11 placentae that had been determined to be negative for CMV during routine pathological examination. IS-PCR demonstrated the presence of CMV DNA in all cell types within placental villi, and IS RT-PCR further defined this result by identifying viral transcripts from all stages of replication. CMV DNA and RNA were shown to be highly concentrated in placental trophoblast cells. The infecting viruses were detected with primers specific for the major immediate early section of the genome (UL122/123), the UL21.5 virion gene, and the glycoprotein B (gB) gene and were determined to be predominantly genotype gB2. Therefore, maternal and fetal host factors, as well as viral load and possibly viral genotype, may all affect the outcome of placental CMV infection.CONCLUSION. Placental villi are involved in the transfer of blood from maternal to fetal circulation. Infection and replication of CMV within placental trophoblasts suggests that these structures may be involved in the transmission of CMV.