Human chorionic gonadotropin induces human macrophages to form intracytoplasmic vacuoles mimicking Hofbauer cells in human chorionic villi.

The most characteristic morphological feature of macrophages in the stroma of placental villi, known as Hofbauer cells, is their highly vacuolated appearance. They also show positive immunostaining for human chorionic gonadotropin (hCG) and express messenger ribonucleic acid of the luteinizing hormone/chorionic gonadotropin receptor with a deletion of exon 9 (LH/CG-R Δ9). Maternal hCG enters fetal plasma through the mesenchyme of the placental villi and promotes male sexual differentiation in early pregnancy; therefore, excess hCG may induce aberrant genital differentiation and hCG must be adjusted at the fetomaternal interface. We hypothesized that hCG is regulated by Hofbauer cells and that their peculiar vacuoles are involved in a cell-specific function. To assess the morphological modification and expression of LH/CG-R Δ9 in human macrophages after hCG exposure, the present study examined phorbol 12-myristate 13-acetate (PMA)-treated THP-1 cells, a human monocyte-macrophage cell line. hCG induced transient vacuole formation in PMA-treated THP-1 cells, morphologically mimicking Hofbauer cells. Immunocytochemistry showed that PMA-treated THP-1 cells incorporated hCG but not luteinizing hormone or follicle-stimulating hormone. Western blotting analyses demonstrated that PMA-treated THP-1 cells expressed an immunoreactive 60-kDa protein, designated as endogenous LH/CG-R Δ9. hCG induced a transient reduction in the LH/CG-R Δ9, which was synchronous with the appearance of cytoplasmic vacuoles. In conclusion, human macrophages regulating hCG via cytoplasmic LH/CG-R Δ9 mimic the morphological characteristics of Hofbauer cells. Their vacuoles may be associated with their cell-specific function to protect the fetus from exposure to excess maternal hCG during pregnancy.