IL-15, a novel cytokine produced by human fetal membranes, is elevated in preterm labor

Interleukin (IL)-15 is a novel cytokine known to have functions similar to those of IL-2 in the cell-mediated immune response. The objectives of this study were to determine whether IL-15 levels change in labor or preterm labor and to identify the regulatory agents and the site of production of IL-15.

Amniochorionic membranes were cultured in an organ explant system and were stimulated with lipopolysaccharides (LPSs). Samples were subjected to reverse transcriptase-polymerase chain reaction (RT-PCR) using specific primers for IL-15 and IL-2. The localization of mRNA and protein was accomplished by in situ hybridization and immunocytochemistry. IL-15 was measured in culture media and amniotic fluid from term and preterm gestations by enzyme-linked immunoadsorbent assay (ELISA).

RT-PCR indicated the expression of IL-15 mRNA in the amniochorion. In situ hybridization and immunocytochemistry documented that mRNA and peptide for IL-15 are found in amnion, chorion, and decidual cells. ELISA results indicated no significant increase of IL-15 peptides in the culture media after LPS stimulation. Maximum levels of this cytokine were seen in the amniotic fluid (AF) of women with preterm labor compared to term labor. AF levels were not higher in preterm-labor patients with proved infection compared with those without infection. RT-PCR-based detection also showed the presence of two isoforms of IL-15 mRNA known to code for two different leader peptide sequences. IL-2 mRNA expression was not observed in the fetal membranes.

The presence of IL-15 mRNA and peptide in the amniochorion and decidua and its increased presence in the AF during preterm labor suggests a possible role for IL-15 in preterm labor. Amniochorion is also shown to possess two IL-15 isoform leader sequences, the differential expression of which may be involved in the regulation of IL-15 secretion.