Role of cytokines in preterm labour and brain injury

Abstract

Intrauterine infection induces an intra‐amniotic inflammatory response involving the activation of a number of cytokines and chemokines which, in turn, may trigger preterm contractions, cervical ripening and rupture of the membranes. Infection and cytokine‐mediated inflammation appear to play a prominent role in preterm birth at early gestations (<30 weeks). The role of infection/inflammation in preterm birth in Europe has been incompletely characterised. The rate of preterm birth in Sweden is lower, and the rate of chorioamnionitis, bacterial vaginosis (BV), neonatal sepsis, and urinary tract infections during pregnancy is lower compared with the USA. In a Swedish population of women with preterm labour or preterm premature rupture of the membranes (PPROM) <34 weeks of gestation, microorganisms were detected in the amniotic fluid in 25% of women with PPROM and in 16% of those in preterm labour. Nearly half of these women had intra‐amniotic inflammation defined as elevated interleukin‐6 (IL‐6) and IL‐8, and there was a high degree of correlation between cytokine levels and preterm birth or the presence of microbial colonisation. These data do not support the hypothesis that infection‐related preterm birth is less frequent in northern Europe than elsewhere. The intra‐amniotic inflammatory response has also been associated with white matter injury and cerebral palsy. We find that in experimental models, induction of a systemic inflammatory response using lipopolysaccharide activates toll‐like receptors (TLRs), which produce either white matter lesions or increase brain susceptibility to secondary insults. Recently, IL‐18 in umbilical blood was shown to correlate with brain injury in preterm infants and IL‐18 deficiency in mice decreases CNS vulnerability.