BACKGROUND: Human pregnancy presents a unique physiological state that allows for growth of an antigenically dissimilar foetus. The immune system plays a key role in establishing and maintaining successful pregnancy, yet detailed understanding of immunological responses in pregnancy is lacking. METHODS: We defined the immunological landscape in pregnancy by screening >350 markers on NK cells, CD4+, CD8+ and γδ T cells, B cells and monocytes in third-trimester pregnancy peripheral blood, cord blood and decidua, and by performing single-cell RNA sequencing (scRNAseq), including 130 CITE-seq antibodies, on NK cells from the blood and decidua of third-trimester pregnancies. We validated our findings in additional blood and decidua samples from first- and third-trimester pregnancies. Blood samples from non-pregnant women were used as a control group for comparison. FINDINGS: Our multiomic approaches revealed altered surface proteomes in lymphoid and myeloid immune subsets during third-trimester pregnancy, in comparison to non-pregnant women. In the blood during pregnancy, circulating NK cells displayed increased SOCS1 (FDR < 0.001) and AREG (FDR < 0.001), both involved in tightly regulating immune responses, as well as HLA-D family (FDR < 0.05-0.0001) gene expression, with increased CCR5 (p < 0.01-0.001) and HLA-DR (p < 0.01-0.001), and decreased CD9 (p < 0.001), CD36 (p < 0.05-0.001), and CX3CR1 (p < 0.05) at the protein level, validated in samples from first- and third-trimester pregnancies. Our analysis of decidual NK (dNK) cells demonstrated a decline in the dNK1 subset between first-trimester decidua and third-trimester decidua basalis (p < 0.0001) and parietalis (p < 0.01), and identified an adaptive-like subset with high expression of cytotoxic molecules, which could be distinguished from the previously described dNK1-3 subsets and was enriched in decidua from women with a history of cytomegalovirus infection (p < 0.05). Functionally, we observed enhanced control of IFN-γ secretion in response to proinflammatory IL-12/IL-18 cytokines in pregnancy (p < 0.05-0.01), however induction of SOCS1 protein expression remained similar between pregnant and non-pregnant women. INTERPRETATION: Overall, our study provides key insights into immunity in pregnancy and reveals fundamental differences in the NK cell compartment. Understanding pregnancy-specific immunology fills important knowledge gaps to better inform the rational design of vaccines, immunotherapies and identification of biomarkers for safe pregnancy outcomes. FUNDING: Australian National Health and Medical Research Council, Australian Medical Research Future Fund, and the National Institute of Allergy and Infectious Diseases.

Mr

Calvin Xu

Research Officer

Department of Microbiology and Immunology

Mr

Calvin Xu

Contact Calvin Xu

Division

Faculty of Medicine, Dentistry and Health Sciences

Mr

Calvin Xu

Print

Calvin Xu's Short Profile

Enquiries

Contact