It is axiomatic that uterine infection raises the risk of preterm labour and postnatal respiratory disorder; however, recent work suggests that components of the inflammatory response may actively promote antenatal lung maturation (Moss et al. 2002). We sought to determine whether an inflammatory stimulus (E. coli lipopolysaccharide, LPS) impacts mesenchyme-epithelium differentiation through cytokine signalling pathways in the pseudoglandular lung.

Lung lobes (extracted following humane killing procedures) from gestation day 16 rat fetuses were mounted onto Whatman nucleopore track-etch filters (8 mm pore) floating on 2 ml of serum-free DMEM/Hams F12 and were maintained in variable O₂ incubators at either fetal (23 mmHg) or ambient (142 mmHg) P_O2. Net change relative to 0 h culture in airway terminal bifurcation, oligonucleosome and lactate dehydrogenase release were used respectively as morphogenic, apoptotic and necrotic indices. TNFα, IL-1β and IL6 were measured by enzyme-linked immuno-absorbent sandwich assay.

Over 120 h, explants at fetal P_O2 showed a net 67.3 ± 2.7 % (mean ± S.E.M.) increase in airway terminal bifurcation, whereas those at ambient P_O2 showed a net 65.2 ± 6.20 % reduction. Addition of 0.5-50 mg ml^-1 LPS did not alter bifurcation at ambient P_O2, but caused a significant reduction at fetal P_O2 at 50 mg ml^-1 LPS (P < 0.05, ANOVA; post-hoc Tukey’s HSD, n = 10). No net shift in necrosis or apoptosis occurred, suggesting a regulated reduction in mesenchyme-epithelium differentiation. To manipulate LPS-evoked TNFα, IL6 and IL-1β release, explants were exposed to 50 mg ml^-1 LPS plus 0.1-1000 nM of Zn²⁺-conjugated thymulin at fetal or ambient P_O2. At either P_O2, thymulin significantly suppressed the release of TNFα at 0.1 nM (P < 0.05, ANOVA; post-hoc Tukey’s HSD, n = 5), but did not alter IL6 or IL-1β release. This was associated with conserved mesenchyme mass without net change in necrosis or apoptosis.

We hypothesised that IL6 signalling via its nuclear factor, CCAAT enhancer binding protein (C/EBP)β, modulates fibroblast growth factor-9 (FGF-9) expression, a regulator of mesenchyme differentiation (Colvin et al. 2001). FGF-9 immunoprecipitate recovery was elevated over ambient P_O2 controls by 50 mg ml^-1 LPS, LPS + 1 mM thymulin, 10 ng ml^-1 recombinant rat IL6 and fetal P_O2. C/EBPβ DNA binding activity matched the FGF-9 expression pattern and these effects were abrogated by rat IL6 antisense oligonucleotide. Explant immunostaining revealed an enhanced mass of FGF-9 and C/EBPβ positive mesenchyme in LPS+thymulin-treated explants over LPS alone. The demonstration that FGF-9 expression may be modulated by LPS-evoked IL6 signalling suggests that uterine infection during pregnancy is likely to alter the course of normal fetal lung morphogenesis.

This work was supported by the MRC (S.C.L.) and the Anonymous Trust.

All procedures accord with current UK legislation.