Immunohistochemical study of human placental stromal cells.

An immunohistochemical study of stromal cells in human placental villi was made using various polyclonal and monoclonal antibodies. This study demonstrated that almost all villous stromal cells expressed HLA-ABC, which is indicative of class I major histocompatibility complex, and vimentin, which is a mesenchymal marker, through the entire period of pregnancy. Some of these stromal cells were considered to be fetal macrophages having HLA-DR, which is a determinant of class II major histocompatibility complex, particularly in the second and third trimesters. Such macrophages also expressed CD-4 (Leu-3a and -3b) and 2H4, which are the cell membrane determinants of suppressor-inducer T lymphocyte; CD-2 (Leu-5b), which is a marker of pan-T cell; Leu-M3, Leu-M5 and Mac-1, which are the markers of monocyte and macrophage lineage; leukocyte common antigen, which is a marker of bone marrow derived cell; and alpha-antichymotrypsin, which is a glycoprotein associated with macrophages. Morphologically, villous macrophages consisted of heterogeneous phenotypes such as classic Hofbauer cells, fibroblast-like spindle cells with long cytoplasmic processes, and dendritic-shaped cells. These may have more complex features than previously considered and may have a greater initiating role in immunologic interactions between mother and fetus when compared with the very sparsely distributed T or B lymphocytes.