315 Localization and differential expression of HLA-G in term human fetal membranes

Abstract

Pregnancy requires immunologic tolerance to support the semiallogenic fetus. HLA-G, a non-classical type I MHC molecule, plays an immunomodulatory role and its expression is reported in placental extravillous trophoblasts. This study localized HLA-G in human fetal membrane cell layers and determined its differential expression in term not in labor (TNIL) or term labor (TL) samples as an indicator of immunologic changes during parturition. Fetal membranes were collected from TNIL (N=6) cesarean and TL (N=6) vaginal deliveries. To localize HLA-G, paraffin embedded sections were immunostained with antibody specific to HLA-G. To determine cell layer and cell type specific HLA-G expression, membranes were divided into amnion and chorion (TNIL [N=4], TL [N=6]) or dispersed and grown as primary cells (amnion epithelial cells [AEC], amnion mesenchymal cells [AMC], chorion trophoblast cells [CTC], decidual cells [DEC]). Protein extracts from layers or cells were analyzed by western blot to determine difference in HLA-G expression between TL and TNIL samples. BeWo (choriocarcinoma cell lines) were used as negative control. Regardless of labor status, amnion and chorion express HLA-G. Although not quantitative, staining intensity was higher in chorion (Fig 1). This was confirmed by western blot. Chorion and CTC had higher HLA-G expression than amnion and AEC; AMC of the membrane matrix were negative for HLA-G (Fig 2a). Quantitative differences were not observed between TNIL and TL in any of the cell types expressing HLA-G (Fig 2b). Decidual layer and BeWo cells were negative for HLA-G. This is the first report to localize HLA-G to the components of the fetal membrane and demonstrates that HLA-G is expressed predominantly in chorion and to a lesser extent in amnion. HLA-G in the membrane likely contributes to immune regulation in pregnancy. Lack of change at term suggests that expression is constitutive in the membrane and differential expression is not a prerequisite for parturition.View Large Image Figure ViewerDownload Hi-res image Download (PPT)