Quantified colocalization reveals heterotypic histocompatibility class I antigen associations on trophoblast cell membranes: relevance for human pregnancy.

Human placental syncytiotrophoblasts lack expression of most types of human leukocyte antigen (HLA) class I and class II molecules; this is thought to contribute to a successful pregnancy. However, the HLA class Ib antigens HLA-G, -E, and -F and the HLA class Ia antigen HLA-C are selectively expressed on extravillous trophoblast cells, and they are thought to play a major role in controlling feto-maternal tolerance. We have hypothesized that selective expression, coupled with the preferential physical association of pairs of HLA molecules, contribute to the function of HLA at the feto-maternal interface and the maternal recognition of the fetus. We have developed a unique analytical model that allows detection and quantification of the heterotypic physical associations of HLA class I molecules expressed on the membrane of human trophoblast choriocarcinoma cells, ACH-3P and JEG-3. Automated image analysis was used to estimate the degree of overlap of HLA molecules labeled with different fluorochromes. This approach yields an accurate measurement of the degree of colocalization. In both JEG-3 and ACH-3P cells, HLA-C, -E, and -G were detected on the cell membrane, while the expression of HLA-F was restricted to the cytoplasm. Progesterone treatment alone induced a significant increase in the expression level of the HLA-G/HLA-E association, suggesting that this heterotypic association is modulated by this hormone. Our data shows that the cell-surface HLA class I molecules HLA-G, -E, and -C colocalize with each other and have the potential to form preferential heterotypic associations.

Interaction between HLA-G and monocyte/macrophages in human pregnancy.

Several lines of evidence suggest that the human leukocyte antigen (HLA)-G play a key role in the regulation of human pregnancy. A sub-population of cells highly represented at the decidua belong to the myeloid-derived monocyte/macrophage lineage, which potentially interact with HLA-G expressing cells. It is proposed that HLA-G protects decidual trophoblasts from lysis by blocking the effector function of decidual monocyte/macrophages. The interaction between HLA-G and monocyte/macrophages may therefore contribute to a successful pregnancy. Here we examine existing knowledge on the convergent role of HLA-G and monocyte/macrophages in pregnancy and define the synergy that exists between these two elements in the decidua. Key features of the HLA-G gene product are discussed followed by the main characteristics of decidual monocyte/macrophages. A hypothetical model for the interaction between HLA-G and monocyte/macrophage cells at the fetal-maternal interface is proposed.

In vivo dendritic cell depletion reduces breeding efficiency, affecting implantation and early placental development in mice.

Implantation of mammalian embryos into their mother's uterus ensures optimal nourishment and protection throughout development. Complex molecular interactions characterize the implantation process, and an optimal synchronization of the components of this embryo-maternal dialogue is crucial for a successful reproductive outcome. In the present study, we investigated the role of dendritic cells (DC) during implantation process using a transgenic mouse system (DTRtg) that allows transient depletion of CD11c+ cells in vivo through administration of diphtheria toxin. We observed that DC depletion impairs the implantation process, resulting in a reduced breeding efficiency. Furthermore, the maturity of uterine natural killer cells at dendritic cell knockout (DCKO) implantation sites was affected as well; as demonstrated by decreased perforin expression and reduced numbers of periodic-acid-Schiff (PAS)-positive cells. This was accompanied by disarrangements in decidual vascular development. In the present study, we were also able to identify a novel DC-dependent protein, phosphatidylinositol transfer protein beta (PITPbeta), involved in implantation and trophoblast development using a proteomic approach. Indeed, DCKO mice exhibited substantial anomalies in placental development, including hypocellularity of the spongiotrophoblast and labyrinthine layers and reduced numbers of trophoblast giant cells. Giant cells also down-regulated their expression of two characteristic markers of trophoblast differentiation, placental lactogen 1 and proliferin. In view of these findings, dendritic cells emerge as possible modulators in the orchestration of events leading to the establishment and maintenance of pregnancy.

Analysis of HLA-G in maternal plasma, follicular fluid, and preimplantation embryos reveal an asymmetric pattern of expression.

Soluble HLA-G (sHLA-G) secretion by human preimplantation embryos in culture has been associated with successful embryo development, and therefore has potential to serve as a noninvasive marker of embryo viability. We have examined the spatial and temporal expression of HLA-G in embryos of varying developmental competence and the role of maternal factors in human embryonic HLA-G expression. Embryos that reached blastocyst stage on day 5 showed a higher frequency of sHLA-G secretion than those at morula or arrested stages (p < 0.05). There was no significant difference in sHLA-G secretion between normal embryos and those diagnosed as chromosomally abnormal by preimplantation genetic diagnosis. HLA-G detected in maternal plasma and follicular fluid did not appear to correlate with HLA-G expressed in the embryo or embryo supernatants. Confocal microscopy analysis indicated that HLA-G protein expression in embryos was not homogeneous; mostly, it was confined to blastocysts localized on trophectoderm and trophectoderm projections. Single-particle fluorescent imaging analysis of HLA-G on the cell surface of JEG-3 cells showed that HLA-G particles were mostly monomeric, but dimeric and higher order oligomers were also observed. These results suggest that HLA-G play an important role in preimplantation embryo development. However, the observed expression of HLA-G in arrested and chromosomally abnormal embryos indicates that HLA-G testing should be used with caution and in conjunction with conventional methods of embryo screening and selection.