['Dendritic cells (DCs) play an important role in antigen presentation and immunoregulation. Modifications of the immune response during pregnancy require the participation of DC. The aim of this study was to follow-up the changes of DCs in human decidua and their correlations to progesterone (Pg) concentrations.', 'Blood leukocytes were isolated from human decidua and analyzed by flow cytometry for the expression of HLA-DR and CD83 markers. Blood monocytes were cultured to differentiate and mature to DCs in the presence of Pg, estradiol or testosterone and analyzed by flow cytometry.', 'The percentage of mature DCs is increased in human decidua during the 1st trimester. When Pg is added to DCs cultured in vitro the percentage of cells expressing both markers increased in specific and dose-dependent manner.'] Are cD83 monocyte-derived dendritic cells present in human decidua and progesterone induces their differentiation in vitro?