Oncostatin M is produced during pregnancy by decidual cells and stimulatesthe release of HCG

Oncostatin M (OSM) is a member of the interleukin-6 superfamily and a multi functional cytokine that effects the growth and differentiation of many dif ferent cell types. OSM concentrations in the sera of pregnant women were fo und to be significantly higher than those of non-pregnant women. Western bl ot analysis revealed that the OSM protein was present in the decidua and ch orionic tissue in each trimester. Throughout pregnancy, the amount of the O SM protein in the decidua was larger than that in the chorionic tissue. Imm unohistochemistry using an anti-OSM monoclonal antibody demonstrated that O SM was mainly localized in the decidual glands and stroma. OSM transcripts in the decidua and the chorionic tissue were detected during each trimester by reverse transcription-polymerase chain reaction (RT-PCR). The regulatio n of human chorionic gonadotrophin (HCG) release by the placenta in first t rimester stimulated with recombinant OSM was also investigated. Stimulation of the placenta by OSM augmented HCG release in a time- and dose-dependent manner. HCG release induced by recombinant human OSM was completely blocke d by antibodies against OSM and the signal transducer, gp130, but only part ially inhibited by antibodies against the leukaemia inhibiting factor (LIF) receptor. These results suggest that OSM molecules produced by decidual gl ands and stromal cells during pregnancy have an important role in placental endocrine function.