The phenotype of human placental macrophages and its variation with gestational age

The antigenic phenotype of human villous stromal macrophages (MΦs) from first and third trimester placentas was analyzed using a large number of monoclonal antibodies (MAbs) to monocyte (Mo)/MΦ-associated cell membrane determinants. The purpose of this study was to investigate MΦ phenotypic heterogeneity to create a database for the correlation of MΦ phenotype with specific immunologic functions. The results showed that villous stromal mononuclear cells express many cell surface antigens found on Mo and MΦs and that they are morphologically diverse, ranging in appearance from classic Hofbauer cells to spindle-shaped cells with long cytoplasmic processes. Villous stromal MΦs were the numerically dominant cell type in this structure and exhibited some major phenotypic differences from MΦs in other tissues. Comparison of first- and third-trimester placentas revealed variation in antigen expression with increasing gestational age, in particular of class II major histocompatibility complex (MHC) determinants: HLA-DR and HLA-DP antigen density was low on first-trimester villous MΦs and much higher on third-trimester MΦs while HLA-DQ was undetectable in the first trimester but present on cells in third trimester placentas. The CD1 (T6) antigen, found on Langerhans (LH) cells and cortical thymocytes, was detected on villous MΦs by two thirds of the MAbs directed against different epitopes on this determinant. Furthermore, comparison with similar studies of lymphoid tissues showed that villous MΦs and dendritic cells share the expression of a number of other cell surface antigens. Finally, it was shown that MΦs in first- and third-trimester villi exhibit strong reactivity with MAbs (Leu 3a,b) to the CD4 antigen that serves as the receptor for the human immunodeficiency virus (HIV), suggesting that these cells may be a portal of entry or reservoir for this virus in the fetuses of pregnant, HIV+ women.