Introduction: Immature myeloid cells (IMCs) are bone marrow derived cells that normally differentiate into granulocytes, macrophages and dendritic cells (DCs), but expand in malignancy. DCs are antigen presenting cells that regulate the immune response. Both IMCs and DCs were shown to take part in angiogenesis however little is known of their function in the placenta.

Aim: To determine whether alternations in DC and IMC populations precede the onset of delivery in the placenta.

Methods: Pregnancies of C57Bl/6J mice were sacrificed on designated days. Placental cells were immunostained using: anti-CD11b, Gr-1, CD11c, MHCII and CD45.Human placental biopsies from normal vaginal deliveries (NVD) and elective cesarean sections not in labor (CS) were immunostained with anti-CD45, LIN2, HLA-DR, CD33 and CD11c. Samples were analyzed by flow cytometry.

Results: Throughout the latter part of mouse pregnancies the CD45+CD11b+Gr1+-IMC population decreased: 29±9.1% (day12), 30±9.9% (day15), 21±8.1% (day18, n=63, p=0.004) while the CD45+CD11c+MHCII+-DC population increased: 0.87±0.3% (day12), 0.70±0.3% (day15), 1.81±1.3% (day18, n=63, p=0.001).
In human placentas, the CD45+LIN2-HLA-DR-CD33+-IMC population was similar in placentas from NVD (30.6±13.3%) and CS (31.9±12.7%, p=0.77), however the CD45+CD11c+HLA-DR+-DC population was significantly higher in placentas derived from NVD (6.7±3.36%) compared to CS (4.7±1.98%, p=0.03).

Conclusions: The IMC population decreases in the mouse placenta while the DC population increases, peaking just before labor and delivery.
Accordingly, in human placentas the DC population increases prior to labor (NVD), whereas it remains low in the absence of labor (CS).
The intriguing possibility that delivery is preceded by the maturation of IMCs into DCs warrants further studies.

Authors:

Paz Gili, Hantisteanu Shay, Hallak Mordechai, Fainaru Ofer

Laboratory for Reproductive Immunology and IVF Unit, Department of Obstetrics and Gynecology, Hillel Yaffe Medical Center, Faculty of Medicine, Technion – Israel Institute of Technology