The microenvironment of the endometrial immune system is crucial to the success of placental implantation and healthy pregnancy. However, the functionalities of immune cells across various stages of the reproductive cycle have yet to be fully comprehended. To address this, we conducted advanced bioinformatic analyses on 230,049 high-quality single-cell transcriptomes from healthy endometrial samples obtained during the proliferative, secretory, early pregnancy, and late pregnancy stages. Our investigation revealed that proliferative natural killer (NK) cells, a potential source of endometrial NK cells, exhibit the most robust proliferative and differentiation potential during non-pregnant stages. During early pregnancy, NK cells display high oxidative phosphorylation metabolism activity, and together with macrophages and T cells, exhibit a strong type II interferon response. Based on our cell-cell interaction analyses, we identify a large majority of interaction pairs to occur in late pregnancy. Finally, we explored the correlation between stage-specific alterations in transcriptomics and the risk genes of common reproductive diseases, unveiling that MHC class I/II molecules, along with TGFBR1, exhibited the potential to serve as biomarkers. Our study provides insights into the dynamics of the endometrial immune microenvironment during different reproductive cycle stages, thus serving as a reference for detecting pathological changes during pregnancy.

Single-cell transcriptomic analysis of immune cell dynamics in the healthy human endometrium