Human chorionic villous macrophages as a fetal biological shield from maternal chorionic gonadotropin

In addition to its most well characterized biological role in the rescue and maintenance of corpus luteum function, human chorionic gonadotropin (hCG) also stimulates the onset of fetal gonadal steroidogenesis. However, excess hCG is teratogenic to fetal gonadal tissues, and therefore hCG must be tightly regulated. Although there is an anatomical barrier between the fetal vessels and maternal blood, other mechanisms may regulate hCG levels. In the present study, we investigated whether human chorionic villous macrophages degraded maternal hCG. Isolated human macrophages incorporated and degraded hCG in a time-dependent manner. Human placental villous macrophages and phorbol myristate acetate (PMA)-treated THP-1 cells expressed the gene encoding an exon 9-deleted form of the luteinizing hormone/chorionic gonadotropin (LH/CG) receptor; expression of the full-length receptor was not determined. While both PMA-treated or untreated THP-1 cells could uptake hCG into their cytoplasms, hCG degradation and excretion of its byproducts only progressed in PMA-treated THP-1 cells. In conclusion, hCG internalization and degradation are different processes in macrophages that protect fetal gonadogenesis from excess hCG. The exon 9-deleted LH/CG receptor, but not the full-length receptor, is involved in the degradation of cytoplasmic hCG by organ-specific, dominant-negative interactions.