The syncytiotrophoblast (STB) of human placenta constitutively and throughout pregnancy produces and secretes exosomes - nanometer-sized membrane-bound extracellular vesicles from the endosomal compartment that convey cell-cell contact ‘by proxy’ transporting information between donor and recipient cells locally and at a distance. Released in the maternal blood, STB-derived exosomes build an exosomal gradient around the feto-placental unit acting as a shield that protects the fetus from maternal immune attack. They carry signal molecules and ligands that comprise distinct immunosuppressive protein signatures which interfere with maternal immune mechanisms, potentially dangerous for the ongoing pregnancy. We discuss three immunosuppressive signatures carried by STB exosomes and their role in three important immune mechanisms 1) NKG2D receptor–mediated cytotoxicity, 2) apoptosis of activated immune cells and 3) PD-1-mediated immunosuppression and priming of T regulatory cells. A schematic presentation is given on how these immunosuppressive protein signatures, delivered by STB exosomes, modulate the maternal immune system and contribute to the development of maternal-fetal tolerance.

Problem: To get a comprehensive picture of cytokine expression in health and disease is difficult, cytokines are transiently and locally expressed, and protein analyses are burdened by biological modifications, technical issues, and sensitivity to handling of samples. Thus, alternative methods, based on molecular techniques for cytokine mRNA analyses, are often used. We compared cytokine mRNA and protein expression to evaluate whether cytokine mRNA profiles can be used instead of protein analyses.Method of study: In kinetic experiments, cytokine mRNA and protein expression of IL‐1β, IL‐6, IL‐8, TNF‐α, and TNF‐β/LTA were studied using real‐time RT‐qPCR and Luminex^® microarrays in the ovarian cancer cell lines OVCAR‐3, SKOV‐3 and the T‐cell line Jurkat, after activation of transcription by thermal stress. In addition, we analyzed IL‐6 and IL‐8 mRNA and protein in a small number of ovarian cancer patients.Results: Ovarian cancer cells can express cytokines on both mRNA and protein level, with 1‐4 hours’ time delay between the mRNA and protein peak and a negative Spearman correlation. The mRNA and protein expression in patient samples was poorly correlated, reflecting previous studies.Conclusion: Cytokine mRNA and protein expression levels show diverging results, depending on the material analyzed and the method used. Considering the high sensitivity and reproducibility of real‐time RT‐qPCR, we suggest that cytokine mRNA profiles could be used as a proxy for protein expression for some specific purposes, such as comparisons between different patient groups, and in defining mechanistic pathways involved in the pathogenesis of cancer and other pathological conditions.

Endometriosis, affecting 10% of women, is defined as implantation, survival, and growth of endometrium-like/endometriotic tissue outside the uterine cavity, causing inflammation, infertility, pain, and susceptibility to ovarian cancer. Despite extensive studies, its etiology and pathogenesis are poorly understood and largely unknown. The prevailing view is that the immune system of endometriosis patients fails to clear ectopically disseminated endometrium from retrograde menstruation. Exosomes are small extracellular vesicles that exhibit immunomodulatory properties. We studied the role of endometriotic tissue–secreted exosomes in the pathophysiology of endometriosis. Two exosome-mediated mechanisms known to impair the immune response were investigated: 1) downregulation of NKG2D-mediated cytotoxicity and 2) FasL- and TRAIL-induced apoptosis of activated immune cells. We showed that secreted endometriotic exosomes isolated from supernatants of short-term explant cultures carry the NKG2D ligands MICA/B and ULBP1-3 and the proapoptotic molecules FasL and TRAIL on their surface, i.e., signature molecules of exosome-mediated immune suppression. Acting as decoys, these exosomes downregulate the NKG2D receptor, impair NKG2D-mediated cytotoxicity, and induce apoptosis of activated PBMCs and Jurkat cells through the FasL- and TRAIL pathway. The secreted endometriotic exosomes create an immunosuppressive gradient at the ectopic site, forming a “protective shield” around the endometriotic lesions. This gradient guards the endometriotic lesions against clearance by a cytotoxic attack and creates immunologic privilege by induction of apoptosis in activated immune cells. Taken together, our results provide a plausible, exosome-based mechanistic explanation for the immune dysfunction and the compromised immune surveillance in endometriosis and contribute novel insights into the pathogenesis of this enigmatic disease.

Problem From conception, a delicate regulation of galectins, a family of carbohydrate‐binding proteins, is established to ensure maternal immune tolerance in pregnancy. Though galectin‐3 (gal‐3), the only chimera type galectin, is abundantly expressed at the feto‐maternal interface; the physiological role of this lectin during pregnancy remains to be fully elucidated and requires further investigation. Method of study In this study, we analyzed serum gal‐3 levels during the course of healthy gestation. Trophoblast functions were evaluated upon gal‐3 exogenous stimulation using trophoblastic cell lines (e.g. HIPEC65, SGHPL‐4 and BeWo cells). Finally, we investigated variations in peripheral gal‐3 levels associated with the development of spontaneous abortion and gestational diabetes mellitus (GDM). Results Gal‐3 circulating levels increased as normal pregnancy progressed. In vitro experiments showed that exogenous gal‐3 positively regulated trophoblast functions inducing invasion, tube formation and fusion. Compared with normal pregnant women, circulating gal‐3 levels were significantly decreased in patients who developed GDM. Conclusion Our results reveal a physiological role for gal‐3 during pregnancy, promoting proper trophoblast functions associated with healthy gestation. GDM is associated with a failure to increase circulating gal‐3 levels late in gestation. Thus, dysregulation of gal‐3 may indicate a contribution of the chimera‐type lectin to this adverse pregnancy outcome.