During pregnancy, the maternal immune system is challenged by the presence of the fetus, which must be tolerated despite being semiallogeneic. Uterine mucosal (or decidual) macrophages (Mϕ), one of the major leukocyte populations at the fetal–maternal interface, have been implicated in fetal tolerance, but information regarding their regulation is scarce. In this study, we investigated the role of several factors potentially involved in the differentiation and polarization of decidual Mϕ with an in vitro Mϕ differentiation model. By using flow cytometry, we showed that M-CSF and IL-10 were potent inducers of M2 (immunoregulatory) Mϕ markers expressed on human decidual Mϕ (CD14, CD163, CD206, CD209). In contrast, proinflammatory stimuli, and unexpectedly also the Th2-associated IL-4 and IL-13, induced different patterns of expression, indicating that a Th2-dominated environment is not required for decidual Mϕ polarization. M-CSF/IL-10–stimulated and decidual Mϕ also showed similar cytokine secretion patterns, with production of IL-10 as well as IL-6, TNF, and CCL4. Conversely, the proinflammatory, LPS/IFN-γ–stimulated Mϕ produced significantly higher levels of TNF and no IL-10. We also used a gene array with 420 Mϕ-related genes, of which 100 were previously reported to be regulated in a global gene expression profiling of decidual Mϕ, confirming that M-CSF/IL-10–induced Mϕ are closely related to decidual Mϕ. Taken together, our results consistently point to a central role for M-CSF and in particular IL-10 in the shaping of decidual Mϕ with regulatory properties. These cytokines may therefore play an important role in supporting the homeostatic and tolerant immune milieu required for a successful pregnancy.

BackgroundAlthough uterine macrophages are thought to play an important regulatory role at the maternal-fetal interface, their global gene expression profile is not known.Methodology/Principal FindingsUsing micro-array comprising approximately 14,000 genes, the gene expression pattern of human first trimester decidual CD14+ monocytes/macrophages was characterized and compared with the expression profile of the corresponding cells in blood. Some of the key findings were confirmed by real time PCR or by secreted protein. A unique gene expression pattern intrinsic of first trimester decidual CD14+ cells was demonstrated. A large number of regulated genes were functionally related to immunomodulation and tissue remodelling, corroborating polarization patterns of differentiated macrophages mainly of the alternatively activated M2 phenotype. These include known M2 markers such as CCL-18, CD209, insulin-like growth factor (IGF)-1, mannose receptor c type (MRC)-1 and fibronectin-1. Further, the selective up-regulation of triggering receptor expressed on myeloid cells (TREM)-2, alpha-2-macroglobulin (A2M) and prostaglandin D2 synthase (PGDS) provides new insights into the regulatory function of decidual macrophages in pregnancy that may have implications in pregnancy complications.Conclusions/SignificanceThe molecular characterization of decidual macrophages presents a unique transcriptional profile replete with important components for fetal immunoprotection and provides several clues for further studies of these cells.

Citation Rodríguez‐Martínez H, Kvist U, Ernerudh J, Sanz L, Calvete JJ. Seminal Plasma Proteins: What Role Do They Play? Am J Reprod Immunol 2011; 66 (Suppl. 1): 11–22Problem  Semen is a heterogenous and complex cell suspension in a protein‐rich fluid with different functions, some of them well known, others still obscure.Method of study  This paper reviews, comparatively, our current knowledge on the growing field of proteomics of the SP and its relevance in relation to the in vivo situation, for the sake of reproductive biology, diagnostics and treatment.Results  Ejaculated spermatozoa, primarily bathing in cauda epididymal fluid, are (in vitro) bulky, exposed to most, if not all, secretions from the accessory sexual glands. In vivo, however, not all spermatozoa are necessarily exposed to all secretions from these glands, because sperm cohorts are delivered in differential order and bathe in seminal plasma (SP) with different concentrations of constituents, including peptides and proteins. Proteins are relevant for sperm function and relate to sperm interactions with the various environments along the female genital tract towards the oocyte vestments. Specific peptides and proteins act as signals for the female immune system to modulate sperm rejection or tolerance, perhaps even influencing the relative intrinsic fertility of the male and/or couple by attaining a status of maternal tolerance towards embryo and placental development.Conclusions  Proteins of the seminal plasma have an ample panorama of action, and some appear responsible for establishing fertility.

A successful pregnancy requires that the maternal immune system is instructed to a state of tolerance to avoid rejection of the semiallogeneic fetal-placental unit. Although increasing evidence supports that decidual (uterine) macrophages and regulatory T cells (Tregs) are key regulators of fetal tolerance, it is not known how these tolerogenic leukocytes are induced. In this article, we show that the human fetal placenta itself, mainly through trophoblast cells, is able to induce homeostatic M2 macrophages and Tregs. Placental-derived M-CSF and IL-10 induced macrophages that shared the CD14(+)CD163(+)CD206(+)CD209(+) phenotype of decidual macrophages and produced IL-10 and CCL18 but not IL-12 or IL-23. Placental tissue also induced the expansion of CD25(high)CD127(low)Foxp3(+) Tregs in parallel with increased IL-10 production, whereas production of IFN-gamma (Th1), IL-13 (Th2), and IL-17 (Th17) was not induced. Tregs expressed the suppressive markers CTLA-4 and CD39, were functionally suppressive, and were induced, in part, by IL-10, TGF-beta, and TRAIL. Placental-derived factors also limited excessive Th cell activation, as shown by decreased HLA-DR expression and reduced secretion of Th1-, Th2-, and Th17-associated cytokines. Thus, our data indicate that the fetal placenta has a central role in promoting the homeostatic environment necessary for successful pregnancy. These findings have implications for immune-mediated pregnancy complications, as well as for our general understanding of tissue-induced tolerance.

Funding Agencies|Medical Research Council [K2013-61X-22310-01-4]

In pregnancy, the decidua is infiltrated by leukocytes promoting fetal development without causing immunological rejection. Murine regulatory T (Treg) cells are known to be important immune regulators at this site. The aim of the study was to characterize the phenotype and origin of Treg cells and determine the quantitative relationship between Treg, T-helper type 1 (T(H)1), T(H)2, and T(H)17 cells in first-trimester human decidua. Blood and decidual CD4(+) T cells from 18 healthy first-trimester pregnant women were analyzed for expression of Treg-cell markers (CD25, FOXP3, CD127, CTLA4, and human leukocyte antigen-DR [HLA-DR]), chemokine receptors (CCR4, CCR6, and CXCR3), and the proliferation antigen MKI67 by six-color flow cytometry. Treg cells were significantly enriched in decidua and displayed a more homogenous suppressive phenotype with more frequent expression of FOXP3, HLA-DR, and CTLA4 than in blood. More decidual Treg cells expressed MKI67, possibly explaining their enrichment at the fetal-maternal interface. Using chemokine receptor expression profiles of CCR4, CCR6, and CXCR3 as markers for T(H)1, T(H)2, and T(H)17 cells, we showed that T(H)17 cells were nearly absent in decidua, whereas T(H)2-cell frequencies were similar in blood and decidua. CCR6(+) T(H)1 cells, reported to secrete high levels of interferon gamma (IFNG), were fewer, whereas the moderately IFNG-secreting CCR6(-) T(H)1 cells were more frequent in decidua compared with blood. Our results point toward local expansion of Treg cells and low occurrence of T(H)17 cells. Furthermore, local, moderate T(H)1 activity seems to be a part of normal early pregnancy, consistent with a mild inflammatory environment controlled by Treg cells.