LAUSR

Objective Preterm birth is the leading cause of neonatal morbidity and mortality worldwide. Some preterm births are associated with clinical chorioamnionitis; yet, this condition has been poorly investigated. Herein, we characterized the amniotic fluid cellular immune responses in women with preterm clinical chorioamnionitis. Methods and subjects Amniotic fluid samples were obtained from women with preterm clinical chorioamnionitis and a positive or negative microbiological culture ( n  = 17). The cellular composition of amniotic fluid was evaluated using fluorescence microscopy, scanning and transmission electron microscopy, and flow cytometry. Women without preterm clinical chorioamnionitis were also examined ( n  = 10). Results Amniotic fluid from women with preterm clinical chorioamnionitis and a positive culture had: (1) abundant neutrophils associated with viable and non-viable bacteria, (2) neutrophils performing phagocytosis, (3) neutrophils forming NETs, (4) increased numbers of neutrophils, monocytes/macrophages, and CD4+ T cells, and (5) high expression of IL-1β by neutrophils and monocytes/macrophages. Amniotic fluid from women with preterm clinical chorioamnionitis and proven infection tended to have fewer monocytes/macrophages and CD4+ T cells compared to those without chorioamnionitis. Conclusion We provide the first morphologic and phenotypic characterization of the cellular immune responses in the amniotic cavity of women with preterm clinical chorioamnionitis, a condition associated with adverse neonatal outcomes.