Decidual Natural Killer cells utilize the antimicrobial protein granulysin to control bacterial infection 2226506

Abstract Introduction During pregnancy maternal decidual Natural Killer cells (dNK) balance the competing needs of immunity and maternal-fetal tolerance. While dNK were initially shown to play essential roles in placentation, we recently discovered their unique ability to provide immunity for placental viral and bacterial infections. A particularly intriguing mechanism is the utilization of the anti-microbial protein granulysin (GNLY) by dNK to kill intracellular bacteria without cytotoxicity of the infected trophoblasts. Methods Using primary human dNK isolated from healthy term placental tissues we utilized high dimensional flowcytometry, functional bacterial killing assays, RNA sequencing and computational analysis of several dNK populations to define the molecular and cellular drivers of GNLY expression and the anti-bacterial functions of dNK. Results First we confirmed that similar to dNK in early pregnancy, term pregnancy dNK i) produce GNLY; ii) process GNLY into the 9kDA active GNLY form; iii) secrete GNLY constitutively; iv); directly transfer GNLY into trophoblasts; and v) most importantly have the capacity to kill cell free and intracellular bacteria in a GNLY dependent manner. Utilizing the vast heterogeneity of dNK types at term pregnancy, we performed RNA-sequencing on FACS purified GNLY-neg, GNLY-pos and 9kda GNLY-HI dNK. Differential gene expression and gene set enrichment analysis identified immune activation pathways, dNK receptors, metabolic pathways, transcription factors and proteolytic enzymes uniquely upregulated in 9kda GNLY-HI dNK. Further computational analysis using Nichenet identified several receptor — ligand interactions between dNK and EVT as potential drivers of GNLY expression and anti-microbial activity of dNK. Conclusion These findings support a key role for dNK in providing placental immunity throughout pregnancy. Discovering the drivers of GNLY expression, activation and transfer by dNK contributes to designing therapeutic strategies to prevent placental and congenital infection. Funding Source Cincinnati Children’s Research Foundation RIP award Topic Categories Mucosal and Regional Immunology (MUC)