Investigation of the role of intrauterine interleukin 6 and interleukin 8 in normal early pregnancy and sporadic miscarriage

Abstract

Successful pregnancy requires tight regulation of two important processes: spiral artery remodelling and invasion of uterine tissue by placental extravillous trophoblast (EVT); disruption of these processes occurs in pregnancy complications such as sporadic miscarriage (SM). Maternal factors, including cytokines and growth factors, may play a role in regulating these fundamental events. The biological function of interleukins (IL)-6 and -8 in other physiological processes suggest that these cytokines maybe important mediators in uteroplacental tissues in early pregnancy. The aim of this study was to investigate intrauterine IL-6, IL-8 and their receptors at the fetal-maternal interface in early pregnancy; specifically, to investigate their role in regulation of EVT invasion and spiral artery remodelling events and determine whether levels of cytokines are altered in SM. IL-6, IL-8 and their receptors were localised in placental bed in the first half of pregnancy by immunohistochemistry. CD56+, CD14+, CD10+ and CD8+ cells were isolated from 8-10 and 12-14 weeks gestational age decidua using positive immunomagnetic separation and secretion of IL-6 and IL-8 was measured and compared by ELISA. All decidual cell types investigated secreted both IL-6 and IL-8. Decidual CD14+ cells were the most abundant source of both cytokines. Secretion of IL-6 by CD10+ cells (P=0.005) and IL-8 by CD56+ cells (P=0.02) was higher at 12-14 weeks compared with 8-10 weeks GA. Compared with healthy pregnant decidua, secretion of IL-6 and IL-8 protein by both CD14+ (IL-6 P=0.05; IL-8 P<0.0001) and CD56+ cells ( IL-6 P=0.02; IL-8 P=0.003) was reduced in SM (≤12+6 weeks gestation). The functional role of these cytokines in early pregnancy was assessed with invasion assays and a chorionic plate artery (CpA) model of artery remodelling. IL-6 did not stimulate EVT invasion in vitro but did cause phosphorylation of kinase proteins involved in trophoblast cell signalling and reduced EVT secretion of RANTES. IL-6 and IL-8 both contributed to misalignment of VSMC in CpA (P=0.04; P=0.001 respectively) and IL-6 increased the separation of CpA VSMC layers alone (P=0.02) and combined to its receptor sIL-6Rα (P=0.001). CD56+ and CD14+ leucocytes were observed in the walls of spiral arteries in the first half of pregnancy with CD14+ cells producing increased Ang-2 (P=0.002) and decreased Ang-1 at 12-14 weeks compared with 8-10 weeks GA (P=0.03). Production of IL-6 and IL-8 within the placental bed in early pregnancy and reduced levels in SM, together with their effects on EVT and VSMCs suggests a possible involvement in controlling trophoblast function and contribution in regulating spiral artery remodelling events.