Specific decidual CD14(+) cells hamper cognate NK cell proliferation and cytolytic mediator expression after mucin 1 treatment in vitro.

Mucin 1 (MUC1) forms a glycocalyx on the surface of decidual epithelial cells that needs to be removed for successful embryo attachment. We investigated whether MUC1 affects human early pregnancy decidual CD14(+) cells and their interactions with cognate decidual natural killer (NK) cells. FITC-dextran internalisation, surface and intracellular antigen levels, and proliferation of CD14(+) and/or CD56(+) cells were analysed by flow cytometry. Magnetic separation was used to purify CD56(+) and CD14(+) cells. Uncultured CD14(+) cells expressed a negligible percentage of CD1a and CD83 molecules. They expressed lower levels of CD16, and higher levels of endocytic mannose receptors (MR), dendritic cell-specific intercellular adhesion molecule grabbing non-integrin (DC-SIGN), proinflammatory chemokine CC receptor 5 (CCR5), and CD163 receptor, than their peripheral blood counterparts. Lipopolysaccharide stimulation did not affect FITC-dextran internalisation in CD14(+) cells. MUC1 bound and internalised, in a dose-dependent manner, the carbohydrate recognition domain of MR, increasing the decoy IL-1 receptor type II and decreasing IL-15 expression in CD14(+) cells. In the presence of MUC1-treated macrophages, the expression levels of the proliferation and cytotoxic mediators (perforin, Fas ligand and TNF-related activation-induced ligand or TRAIL) was attenuated, while that of the anti-inflammatory chemokine CCL17 was increased, in NK cells compared with untreated macrophages. In conclusion, MUC1 supports the alternative activation of tissue-specific CD14(+) cells, and may restrict proliferation of NK cells and regulate their content of cytotoxic mediators. Based on the experiments with first-trimester decidual cells in vitro, we conclude that removing MUC1 from decidual tissue might help control trophoblast invasion by NK cells.