AbstractProblemPlacenta accreta (PA) is defined by an abnormal invasion of placental trophoblasts into the myometrium, which can lead to serious postpartum complications. Macrophages play an important role in the regulation of trophoblast function. Both granulocyte colony‐stimulating factor (G‐CSF) and its receptor (granulocyte colony‐stimulating factor receptor, G‐CSFR) have effects on trophoblast invasion. However, the current understanding of G‐CSF secretion, G‐CSFR expression, abnormal polarization of decidual macrophages (dMϕ) in PA and the abnormal invasion of placental trophoblasts into the myometrium are limited.Method of StudyThe polarization of dMϕ in PA was analyzed by flow cytometry (FCM), and the expression of G‐CSFR in placental trophoblasts in PA was evaluated by immunohistochemistry. In an in vitro co‐culture model, we investigated the effects of HTR‐8/SVneo trophoblasts cell line (HTR‐8) on macrophage human monocyte cell line (THP‐1) polarization and G‐CSF secretion, and we also analyzed the effects of THP‐1 cells, especially M2‐like subtype, on primary trophoblasts and HTR‐8 proliferation, invasion, and adhesion. FCM, transwell assays, adhesion assays, and proliferation assays were used in the above model.ResultsCompared with controls (n = 9), dMϕ showed significantly lower levels of M1 markers CD80 and CD86 and higher levels of the M2 markers CD163 and CD206, and G‐CSFR expression of placental trophoblasts was increased in PA (n = 5). In vitro experiments showed that the trophoblast HTR‐8 cell line induced polarization of THP‐1 cells to an M2‐like subtype and increased their secretion of G‐CSF. Furthermore, IL‐4/IL‐13‐induced M2‐like THP‐1 macrophages were able to increase the expression of G‐CSFR, proliferation, invasion and adhesion of both primary trophoblasts and HTR‐8 trophoblasts.ConclusionsThere is an altered immune imbalance at the maternal‐fetal interface in PA, which further may lead to abnormal trophoblast function. G‐CSF and its receptors may play important roles in abnormal polarization of macrophages and abnormal invasion of trophoblasts.