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Strategically located in mucosal barriers, innate lymphoid cells (ILCs) are relevant in local containment and tolerance of commensal microflora. ILCs have been recently described at the fetomaternal interface, where the development of a semi-allogeneic fetus can only succeed in a well-controlled immune environment. We postulate that ILCs adapt their antigen presentation capacity to protect pregnancy from excessive immune responses. Human ILCs were studied in deciduae of term pregnancies, peripheral blood and in in vitro generated ILCs. Fresh isolated lymphocytes or cells treated with pregnancy-related factors were investigated. The fetal antigen rejection-based CBA/J × DBA/2J mouse model (poor outcome pregnant mice; POPM) was used to characterize ILC antigen presentation potential in normal and immunologically disturbed pregnancies. ILC antigen presentation potential was characterized by flow cytometry and qPCR. We discovered that the distribution of ILC subsets changed during both human and murine pregnancy. Moreover, the pregnancy was accompanied by reduced MHCII expression in splenic ILCs during normal pregnancy (CBA/J × BALB/c; good outcome pregnant mice; GOPM) but increased in splenic and intestinal ILCs of CBA/J × DBA/2J mice. In vitro, splenic ILCs from pregnant mice increased MHCII expression after stimulation with IL-1β and IL-23. In contrast, uterine ILCs displayed lower MHCII expression, which remained unchanged after stimulation. Finally, pregnancy-related factors and hormones present in the uterine environment reduced antigen presentation potential of human ILCs in vitro. Together, these data indicate that, during pregnancy, peripheral and especially uterine ILCs adapt their antigen presenting potential to maintain a level of tolerance and support pregnancy.

Alterations in the immunologic balance during pregnancy have been associated with poor pregnancy outcomes. The underlying mechanisms are complex and mouse models delivered valuable information on inflammatory imbalance in disturbed pregnancies and served as model to test potential anti-inflammatory therapies. CD83 is a transmembrane protein (mCD83) with a soluble form (sCD83) which possesses strong anti-inflammatory properties. During murine pregnancy, upregulated mCD83 expression induces sCD83 release after in vitro stimulation with LPS, phorbol myristate acetate (PMA) and ionomycin. The release mechanism of sCD83 and its control are yet to be elucidated. In this study, the expression of mCD83 and sCD83 has been extensively studied in the CBA/J × DBA/2J mouse model of pro-inflammatory-mediated pregnancy disturbances. mCD83 was higher expressed on splenic B cells, uterus-draining lymph nodes T cells and dendritic cells from mice with poor pregnancy outcome (PPOM) compared to mice with good pregnancy outcome (GPOM). PPOM, however, was accompanied by lower sCD83 serum levels. In vitro treatment of splenic B cells with progesterone led to a reduction of TIMP1 expression, mCD83 expression and sCD83 release, while TIMP1 treatment had a positive effect on sCD83 availability. These results suggest that tissue and matrix components are involved in the regulation of CD83 in murine pro-inflammatory pregnancies.