(24) The Role of IL-9 Signaling in Immune-mediated Preterm Birth

Background: Preterm birth (PTB) affects 1 in 10 pregnancies and is the leading cause of neonatal mortality. The immunological processes underlying PTB include temporal shifts in the balance between maternal-fetal tolerance and proinflammatory signals preceding labor. Regulatory T cells (Tregs) play a central role in maternal-fetal tolerance, and mothers with decreased numbers of Tregs at the maternal-fetal interface are at increased risk for pregnancy complications including PTB. Furthermore, Treg depletion in mice during the 3rd week of an allogeneic pregnancy predisposes to PTB. However, the underlying mechanisms precipitating PTB when Treg abundance/function is decreased remain incompletely understood. Among pathways that are impacted by Treg depletion, there is evidence of increased interleukin-9 (IL-9) signaling. IL-9 is a pleiotropic cytokine with roles in the modulation of inflammatory responses and hematopoiesis. It is of particular interest in PTB as it is one of the most abundant cytokines at the maternal-fetal interface, increases throughout pregnancy, and regulates targets involved in the timing of parturition.

Objectives: We hypothesize that increased IL-9 signaling is integral to the pathophysiology of PTB mediated by Treg depletion.

Design/Methods: We implemented a murine model of immune-mediated preterm birth by Treg depletion in the 3rd week of an allogeneic pregnancy. We used flow cytometry, ELISA, and qPCR to characterize expression of IL-9, IL-9 receptor and downstream targets as well as characterize immune populations in maternal and fetal tissues.

Results: Depletion of Tregs in the third week of murine pregnancy decreases the length of gestation and results in an increased incidence of PTB. Treg-depleted pregnant dams exhibit increased IL-9 signaling as evidenced by increased circulating levels of IL-9, increased IL-9+ T cells, and increased placental expression of IL-9 and its receptor. Furthermore, there are increased levels of IL-9 in the amniotic fluid of fetuses from Treg-depleted pregnancies. Downstream targets of IL-9 known to play a role in the timing of parturition including NLRP3, IL-1β, and arginase-1 exhibit increased expression at the maternal-fetal interface and in the developing fetus.

Conclusions: Using a model of immune-mediated preterm birth, we have shown that increases in IL-9 and its downstream signaling targets are associated with PTB. Future work will focus on elucidating the underlying mechanism to improve our understanding of immune-mediated PTB and identify potential targets and/or biomarkers for future studies.