Surfactant protein-A (SP-A) selectively inhibits prostaglandin F2alpha (PGF2alpha) production in term decidua: implications for the onset of labor.

CONTEXT: Labor is characterized by "decidual activation" with production of inflammatory mediators. Recent data suggest that surfactant protein-A (SP-A) may be critical to the onset of labor in mice. Whether this is also true in humans is unclear.

OBJECTIVES: The aim was to investigate: 1) the expression of SP-A at the maternal-fetal interface; 2) the effect of SP-A on the production of inflammatory mediators by human decidua; and 3) the association between single nucleotide polymorphisms in maternal SP-A genes and spontaneous preterm birth.

RESEARCH DESIGN AND METHODS: In situ expression of SP-A was investigated by immunohistochemistry and quantitative RT-PCR. Term decidual stromal cells were isolated, purified, and treated with/without SP-A (1-100 μg/ml), IL-1β, and/or thrombin. Levels of inflammatory mediators [IL-6, IL-8, TNFα, matrix metalloproteinase-3, monocyte chemotactic protein-1, IL-1β, PGE(2), prostaglandin F(2α) (PGF(2α))] and angiogenic factors (soluble fms-like tyrosine kinase-1, vascular endothelial growth factor) were measured in conditioned supernatant by ELISA and corrected for protein content. The effect of SP-A on eicosanoid gene expression was measured by quantitative RT-PCR.

RESULTS: SP-A localized to endometrium/decidua. High-dose SP-A (100 μg/ml) inhibited PGF(2α) by term decidual stromal cells without affecting the production of other inflammatory mediators, and this effect occurred at a posttranscriptional level. Decidual SP-A expression decreased significantly with labor. Single nucleotide polymorphisms in the SP-A genes do not appear to be associated with preterm birth.

CONCLUSIONS: SP-A is produced by human endometrium/decidua, where it significantly and selectively inhibits PGF(2α) production. Its expression decreases with labor. These novel observations suggest that decidual SP-A likely plays a critical role in regulating prostaglandin production within the uterus, culminating at term in decidual activation and the onset of labor.