Paracrine regulation of distinct trophoblast functions in vitro by placental macrophages

In view of the accumulating evidence for paracrine mechanisms regulating tr ophoblast function: we tested the hypothesis that placental macrophages aff ect trophoblast activity in a paracrine fashion. Trophoblast was isolated f rom 17 term placentas (-IP). One aliquot of cells was further immunopurifie d (+IP) using an HLA class I antibody. This increased the proportion of tro phoblast (+IP >97%; -IP similar to 70%) as identified by rigorous immunocyt ochemistry. Most (similar to 70%) non-trophoblast cells in -IP were macroph ages. The cells were cultured for 5 days with a daily medium change. In add ition, +IP cells from seven placentas were cultured with lipopolysaccharide (LPS)-stimulated or -unstimulated macrophage-conditioned media. The concen trations of lactate, trophoblast-specific hormones, human chorionic gonadot ropin-beta (hCG-beta) and human placental lactogen (hPL), of several prosta noids and of endothelin-l and angiotensin II were determined in the culture media. The accumulated amounts of substances released into the culture med ia, corrected for the greater proportion of trophoblast in +IP cultures, we re on average two- to threefold higher (hCG-beta: 18-fold) in +IP than in - IP, with the exception of endothelin-1,2 (no change), angiotensin II (-70%) and 6-keto-prostaglandin-F-1 alpha (-40%). [H-3]leucine incorporation into the trichloroacetic acid (TCA)-precipitable pool measured on day 5 was two fold higher in +IP than in -IP. Addition of conditioned media reverted thes e changes. The data demonstrate that placental macrophages in culture affec t trophoblast biosynthetic activity in a paracrine fashion. We conclude tha t macrophages are important regulators of trophoblast activity.