Abstract Preterm birth (PTB) affects over 15 million infants yearly. In up to 40% of late PTBs, placental examination reveals chronic chorioamnionitis (CCA), maternal mononuclear cell infiltration in the chorioamniotic membranes; yet, the cellular landscape remains fully unknown. Herein, we first used imaging mass cytometry (IMC) to map the phenotype and spatial distribution of immune cells at the maternal-fetal interface of women with PTB and CCA and non-CCA controls (n = 4 each). Cases exhibited a 5-fold increase in T cells, including effector memory CD4+ (p=0.02) and proliferative CD8+ T cells (p=0.04), and a 7-fold rise in CD163+CD206+ macrophages (p=0.05) compared to controls. NK cells were also present in both groups. Neighborhood analysis revealed that CD8+ T cells are in proximity to macrophages and CD4+Tbet+ T cells, and distanced from NK cells. Next, we performed spatial transcriptomics (STx) in each study group (n = 8 PTB with CCA, n = 7 PTB no CCA). STx highlighted diversity in several clusters of T cells, macrophages, and other immune cells found to be transcriptionally active in CCA. Gene ontology analysis indicated enrichment for CD8+ T cell activation, as well as IL-12 and IFNγ signaling in macrophages in CCA. Ongoing efforts are focused on validation and functional testing of such immune cells in order to unveil the complex interactions at the maternal-fetal interface in CCA, a placenta pathology associated with adverse outcomes in the mother and offspring.
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