Production of secretory leukocyte protease inhibitor by human amniotic membranes and regulation of its concentration in amniotic fluid

Secretory leukocyte protease inhibitor (SLPI) is a potent inhibitor of human leukocyte elastase. SLPI is a protein found in various human fluids, including parotid secretions, cervical mucus, seminal plasma and ascites. Western blot analysis revealed that SLPI protein is detected as a 12 kDa band in both the amniotic fluid and the amniotic membrane. The amniotic fluid concentrations of SLPI were assayed by enzyme-linked immunosorbent assay. SLPI concentrations in the amniotic fluid of women in the third trimester were higher than those in the second trimester. Immunohistochemistry using an anti-SLPI polyclonal antibody revealed positive staining in epithelial cells in amniotic membranes. Reverse transcription-polymerase chain reaction demonstrated that SLPI transcripts could be detected in the amniotic membranes. To determine the mechanism of SLPI production by amniotic cells, purified amniotic cells were stimulated with various cytokines. Amniotic cells produced SLPI in a dose-dependent manner when stimulated with interleukin (IL)-1α, IL-1β, and tumour necrosis factor-α. The present findings show that SLPI is produced by the amniotic membranes in response to cytokine concentrations. The SLPI in the amniotic fluid may contribute to immunodefence mechanisms during pregnancy.