Imaging mass cytometry reveals the prominent role of myeloid cells at the maternal-fetal interface.

Although the immunological complexity of the maternal-fetal interface is well appreciated, the actual interaction of maternal immune cells and fetal trophoblasts is insufficiently understood. To comprehend the composition and spatial orientation of maternal immune cells and fetal extravillous trophoblasts, we applied imaging mass cytometry on decidua basalis of the three trimesters of healthy pregnancy. Within all trimesters, we observed considerably higher frequencies of myeloid cells in the decidua than is seen with single-cell suspension techniques. Moreover, they were the most pronounced cell type in the microenvironment of other decidual cells. In first trimester, HLA-DR- macrophages represented the most abundant myeloid subcluster and these cells were frequently observed in the vicinity of trophoblasts. At term, HLA-DR+ macrophage subclusters were abundantly present and frequently observed in the microenvironment of T cells. Taken together, our results highlight the dynamic role of myeloid cells at the human maternal-fetal interface throughout gestation.

Different immunoregulatory components at the decidua basalis of oocyte donation pregnancies.

Oocyte donation (OD) pregnancies are characterized by more fetal-maternal human leukocyte antigen (HLA) mismatches compared with naturally conceived (NC) and in vitro fertilization (IVF) pregnancies. The maternal immune system has to cope with greater immunogenetic dissimilarity, but involved immunoregulation remains poorly understood. We examined whether the amount of regulatory T cells (Tregs) and immunoregulatory cytokines in decidua basalis of OD pregnancies differs from NC and IVF pregnancies. The cohort included 25 OD, 11 IVF and 16 NC placentas, maternal peripheral blood, and umbilical cord blood of uncomplicated pregnancies. Placenta slides were stained for FOXP3, IL-10, IL-6, gal-1, TGF-ß and Flt-1. Semi-quantitative (FOXP3+ Tregs) and computerized analysis (cytokines) were executed. The blood samples were typed for HLA class I and II to calculate fetal-maternal HLA mismatches. The percentage of Tregs was significantly higher in pregnancies with 4-6 HLA class I mismatches (n = 17), compared to 0-3 mismatches (n = 35; p = 0.04). Cytokine analysis showed significant differences between OD, IVF and NC pregnancies. Flt-1 was significantly lower in pregnancies with 4-6 HLA class I mismatches (p = 0.004), and in pregnancies with 6-10 HLA mismatches in total (p = 0.024). This study suggests that immunoregulation at the fetal-maternal interface in OD pregnancies with more fetal-maternal HLA mismatches is altered.

Visualizing Dynamic Changes at the Maternal-Fetal Interface Throughout Human Pregnancy by Mass Cytometry.

During healthy pregnancy, a balanced microenvironment at the maternal-fetal interface with coordinated interaction between various immune cells is necessary to maintain immunological tolerance. While specific decidual immune cell subsets have been investigated, a system-wide unbiased approach is lacking. Here, mass cytometry was applied for data-driven, in-depth immune profiling of the total leukocyte population isolated from first, second, and third trimester decidua, as well as maternal peripheral blood at time of delivery. The maternal-fetal interface showed a unique composition of immune cells, different from peripheral blood, with significant differences between early and term pregnancy samples. Profiling revealed substantial heterogeneity in the decidual lymphoid and myeloid cell lineages that shape gestational-specific immune networks and putative differentiation trajectories over time during gestation. Uncovering the overall complexity at the maternal-fetal interface throughout pregnancy resulted in a human atlas that may serve as a foundation upon which comprehension of the immune microenvironment and alterations thereof in pregnancy complications can be built.

Increased HLA-G Expression in Term Placenta of Women with a History of Recurrent Miscarriage Despite Their Genetic Predisposition to Decreased HLA-G Levels.

Human leukocyte antigen (HLA)-G is an immune modulating molecule that is present on fetal extravillous trophoblasts at the fetal-maternal interface. Single nucleotide polymorphisms (SNPs) in the 3 prime untranslated region (3'UTR) of the HLA-G gene can affect the level of HLA-G expression, which may be altered in women with recurrent miscarriages (RM). This case-control study included 23 women with a medical history of three or more consecutive miscarriages who delivered a child after uncomplicated pregnancy, and 46 controls with uncomplicated pregnancy. Genomic DNA was isolated to sequence the 3'UTR of HLA-G. Tissue from term placentas was processed to quantify the HLA-G protein and mRNA levels. The women with a history of RM had a lower frequency of the HLA-G 3'UTR 14-bp del/del genotype as compared to controls (Odds ratio (OR) 0.28; p = 0.039), which has previously been related to higher soluble HLA-G levels. Yet, HLA-G protein (OR 6.67; p = 0.006) and mRNA (OR 6.33; p = 0.010) expression was increased in term placentas of women with a history of RM as compared to controls. In conclusion, during a successful pregnancy, HLA-G expression is elevated in term placentas from women with a history of RM as compared to controls, despite a genetic predisposition that is associated with decreased HLA-G levels. These findings suggest that HLA-G upregulation could be a compensatory mechanism in the occurrence of RM to achieve an ongoing pregnancy.