Forkhead box P3 is selectively expressed in human trophoblasts and decreased in recurrent pregnancy loss

Forkhead box P3 (Foxp3) is necessary for induction of the immunosuppressive functions in regulatory T cells. Recent data indicate that some non-lymphoid cells, such as certain tumor cells, also express Foxp3, which participates in tumorigenesis and is related to the invasive and proliferative behavior of the tumor. However, the expression of Foxp3 in trophoblasts has not been studied previously.

Localization of Foxp3 in the villi and decidua in the first trimester was determined using immunohistochemistry. Foxp3 expression was detected by flow cytometry, and the expression levels in the first trimester placenta were compared with those in the term placenta. Additionally, the Foxp3 expression in trophoblasts in recurrent pregnancy loss (RPL) was analyzed by real-time polymerase chain reaction (RT-PCR), immunohistochemistry and Western blot.

Foxp3 is expressed by trophoblasts in early pregnancy in the villi and decidua. Foxp3 is expressed in the nuclei of both trophoblast cell columns and cytotrophoblasts. However, low Foxp3 expression was observed in syncytiotrophoblasts. Foxp3 was also expressed by the extravillous trophoblasts in early pregnancy in decidua. The Foxp3 expression in trophoblasts in the term placenta was significantly decreased compared with that in the normal early pregnancy. Moreover, decreased levels of Foxp3 mRNA and protein were observed in women with RPL.

The selective expression of Foxp3 in human trophoblasts suggest that Foxp3 expression may be associated with the proliferation and invasion behavior of trophoblasts. The decreased Foxp3 expression in the trophoblasts in RPL may contribute to better understanding of the pathological characteristics of RPL.