Trophoblast Apoptosis in Human Placenta at Term as Detected by Expression of a Cytokeratin 18 Degradation Product of Caspase

Abstract

Abstract Context.—Apoptosis occurs in the normal placenta. The monoclonal antibody M30 is directed against a novel epitope of cytokeratin 18 (CK18) that is formed by caspase cleavage early in the apoptotic cascade, and this antibody may therefore be useful for evaluating trophoblast apoptosis. Objective.—We undertook the present study to evaluate the use of monoclonal antibody M30 to assess trophoblast apoptosis in placenta at term. Methods.—We stained paraffin-embedded placental tissues from 15 deliveries at term with M30. We compared positive M30 staining and CK18 staining (as detected by a monoclonal antibody directed against CK18) of trophoblasts in serial slides. We also compared apoptotic rates as detected by M30 and TUNEL (terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick end labeling) in 7 of the placentas. Results.—In fields of villous tissue, most M30-positive cells were CK18-positive syncytiotrophoblasts. Approximately half of M30-positive cells occurred as focal positive staining in the syncytial layer, and half occurred as abundant staining of syncytiotrophoblasts in areas with increased intervillous or perivillous fibrinoid. We found very few M30-positive cells in villous stroma. In decidual/basal plate tissues, most (two thirds) of the M30-positive cells were CK18-positive extravillous trophoblasts, whereas one third were syncytiotrophoblasts of anchoring villi. Since TUNEL detects apoptosis in both epithelial and nonepithelial cells, more cells were positively stained with TUNEL than with M30 in some tissue fields. However, our observations suggest that M30 was more sensitive than TUNEL in recognizing apoptotic trophoblasts and had less nonspecific staining than TUNEL. Conclusion.—We recommend the use of monoclonal antibody M30 for apoptosis studies in placental tissues. This antibody is easy to handle, the staining obtained seems specific, and the nonspecific staining seems negligible.