s / Placenta 36 (2015) 469e521 515 Objective: The aim of the study was to describe the placental microscopic features of the Southern elephant seal, Mirounga leonina. No descriptions of the placentae from the genusMirounga have been found in the available literature. Methods: Placentas from three elephant seals were collected after natural delivery at the Stranger Point rockery, close to the Argentinian Carlini Base scientific research station (South Shetland Islands, Antarctica), during the breeding period, the austral spring terrestrial phase in 2013. Samples were formalin-fixed and processed by histological routine techniques. Vimentin and cytokeratin filaments were immunohistochemically detected using a mouse monoclonal and a rabbit polyclonal antibody, respectively, and revealed with the EnVision® detection system+HRP. Results: As in other carnivores, the choriovitelin placenta of Mirounga leonina is zonary. The anular band showed multiple macroscopic orange areas, both in the margins and in the center of the labyrinth, which corresponded to hemosiderin aggregates located among trophoblast villi. Macroscopic hematomal areas were not observed. Based on chorionic villous arrangements, Mirounga placenta was labyrinthine, reminding the canine placenta. In the chorioallantoic membrane, numerous and remarkably thick fetal arterial vessels were observed. This pospartum placental labyrinth showed scarce and flattened trophoblast cells and was almost composed of maternal and fetal intermingled blood vessels. Fetal vessels were typically small, round and regular in shape whereas maternal vessels were larger and irregular, and exhibited attenuated endothelial cells (unlike those from domestic carnivores) and numerous leukocytes. Fetal vessels were between trophoblast cells resulting in a very thin placental barrier, otherwise endotheliochorial. We did not find vimentin positive cells (other than endothelial cells or circulating leukocytes) similar to decidual cells of the cat placenta. Conclusions: Based on this preliminary study we conclude that Mirounga leonina placenta shares some basic features with that of other carnivores but shows some peculiarities, especially related to the source of iron for the fetuses. PB.30. PROSTAGLANDIN E2 INHIBITS THE PROINFLAMMATORY PHENOTYPE INDUCED BY TGF-b ON MONOCYTE-DERIVED DENDRITIC CELLS Federico Remes Lenicov, Augusto Varese, Antonela Merlotti, Jorge Geffner, Ana Ceballos. Instituto de Investigaciones Biom edicas en Retrovirus y SIDA (UBA-CONICET), Buenos Aires, Argentina Objectives: The immunomodulatory properties of semen are well recognized, but details are lacking regarding its effect on dendritic cells, the immune cells in charge of deciding the type of response against foreign antigens. Previously, we have demonstrated that seminal plasma prostaglandins (PG) induce a tolerogenic profile on monocyte-derived dendritic cells (DCs). Human seminal plasma also contains high amounts of TGF-b, which has been shown to promote a proinflammatory phenotype in DCs. We aim to characterize the interaction between PG and TGF-b during the differentiation of DCs from monocytes. Methods: Seminal plasma was obtained by centrifugation of semen samples donated by healthy volunteers. DCs were obtained by incubating peripheral blood monocytes (>85% purity) with GM-CSF and IL-4 for 5 days, in the absence (control) or presence of TGF-b (TGF-DCs), PGE2 (PGDCs), the combination of these (TGF+PG-DCs) or seminal plasma (SP-DCs). DCs and their ability to expand the CD4+CD25+FoxP3+ lymphocyte population was analyzed by flow cytometry. Cytokine production was measured by ELISA in cell culture supernatants. Results: TGF-DCs showed a marked expression of CD1a and null expression of CD14. Addition of PGE2 (10-9 to 10-6 M) during differentiation of TGF-DCs reversed this phenotype, resulting in CD1a-CD14+ DCs, associated with tolerogenic properties and similar to that obtained for PG-DCs and SP-DCs. Moreover, stimulation of TGF-DCs with LPS resulted in increased production of IL-12p70 and IL-23 compared to control DCs, while TGF+PGDCs were unable to produce IL-12p70 or IL-23 upon stimulation, as observed also for PG-DCs and SP-DCs. Finally, in a mixed-lymphocyte reaction, TGF-DCs suppressed the expansion of CD4+CD25+FoxP3+ cells compared to control DCs. In contrast, we observed increased expansion of this population comparing control DCs with TGF+PG-DCs, PG-DCs and SPDCs. Conclusions: The presence of PGE2 during differentiation abolishes the proinflammatory properties elicited by TGF-b in monocyte-derived DCs. PB.31. POSSIBLE ROLE OF TRPV-1 AND AQPS IN THE REGULATION OF TROPHOBLAST CELL VOLUME Nora Martinez , Julieta Reppetti , Cyntia Ab an , Graciela Moya , Mariana Farina , Alicia E. Damiano . 1 Laboratorio de Fisiopatologia Placentaria, CEFyBO-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina; 2 Laboratorio de Biologia de la Reproducci on, IFIBIO-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina; 3 Fundaci on GENOS, Buenos Aires, Argentina Mammalian cells have homeostatic mechanisms that maintain body-fluid osmolality near 300 mOsm/kg through the intake or excretion of water and salts. This osmoregulation is vital to prevent changes in cell volume that result in irreversible damage. Transient receptor potential vanilloid type-1 (TRPV-1) is a cation channel that mediates Ca2+ influx in response to osmotic stress, acting as a hypertonicity sensor. Recently, we have described TRPV-1 in trophoblast cells. Aquaporins (AQPs) are a family of small integral membrane proteins that facilitate osmotically driven water transport. Although AQP1, AQP3 and AQP9 are highly expressed in trophoblasts during early gestation, their role is still unknown. Objective: To evaluate the contribution of AQPs and TRPV-1 in cell volume regulation of first trimester trophoblast and the consequences on cell viability. Methods: TRPV-1, AQP3 and AQP9 protein expressions were analyzed by Western blot and immunohistochemistry in first trimester human chorionic villous samples (CVS) and in the Swan-71 cell line. The effect of hyperosmolarity on each protein expression was evaluated in Swan-71 cells before and after the inhibition of AQPs with HgCl2. Cell viability was analyzed by MTT assay and cleaved caspase-3 expression. Results: TRPV-1, AQP3 and AQP9 expression was found in CVS and Swan71 cells. After exposure to hyperosmolarity, we observed that the expression of the three proteins increased (p