Characterization of the sugar chain expression of normal term human placental villi using lectin histochemistry combined with immunohistochemistry.

The general sugar expression pattern was studied in 9 normal full-term human placentas by the use of 21 individual lectins in combination with immunohistochemistry for various markers to understand the function of the placenta as the site of feto-maternal interactions. In mature intermediate and terminal villi, the brush border of the syncytiotrophoblast layer strongly expressed GlcNAc (as stained by WGA, S-WGA, DSL lectins) but weakly expressed sialic acid (Mal II, SNA). The cytoplasm of the syncytiotrophoblast layer showed weak expressions of GlcNAc and Gal/GalNAc with granular patterns. The cytotrophoblast layer, as also recognized by PCNA and HAI-1, typically expressed GlcNAc (LEL etc.) and Gal/GalNAc (MAL I). We found that the cytotrophoblast layer became very thin but largely maintained its continuity in the mature villi. The basement membranes of both the trophoblast layer and the endothelial layer strongly and continuously expressed mannose (Con A, LCA) and galactose (ECL, RCA I). Although endothelial cells almost exclusively expressed sialic acid and fucose, UEA I showed a heterogeneous reactivity with endothelial cells within the same vessels. No uniform expression pattern of any sugar was seen in stromal components except for Hofbauer cells, which usually expressed GlcNAc (LEL and DSL etc.). Thus, the sugar expression analysis by lectin histochemistry combined with immunohistochemistry proved helpful to understand the sugar chain related functions of the placenta under both normal and pathological conditions.