Secretory leukocyte protease inhibitor concentration increases in amniotic fluid with the onset of labour in women: characterization of sites of release within the uterus

Secretory leukocyte protease inhibitor is a potent inhibitor of neutrophil function, a mediator of mucosal immunity and an inhibitor of NF kappa B regulated inflammatory responses. However, its source, function and regulation within the uterus during pregnancy and at parturition are not well defined. In amniotic fluid, the concentration of secretory leukocyte protease inhibitor increased significantly from 2nd trimester (24 +/- 3 ng/ml; mean +/- S.E.M.; n=20) to term (751 +/- 53 ng/ml; P<0.05; n=15) with a further profound increase (P<0.005) with the onset of labour (3929 +/- 1076 ng/ml; n=15). To establish the intrauterine sites of secretion, explants (n=6 different patients per tissue) were collected at term after elective caesarean section. High levels of secretory leukocyte protease inhibitor were released by decidua (135.2 +/- 12.4 pg/mg; mean +/- S.E.M.) and chono-decidua (325.1 +/- 26.4 pg/mg) with less by amnion (55.6 +/- 6.0 pg/mg) and placenta (9.2 +/- 1.9 pg/mg). Intense immunoreactivity for secretory leukocyte protease inhibitor was detected predominantly in decidua parietalis cells adherent to the chorion laeve and myometrium, and also in decidua basalis. We propose that, within the pregnant uterus, secretory leukocyte protease inhibitor is released by decidua, fetal membranes and potentially the fetal lung. The increase in secretory leukocyte protease inhibitor may act to modulate proinflammatory paracrine interactions for the maintenance of pregnancy and limit those occurring at parturition within the uterus.