Comparative study of placental protein 19, human chorionic gonadotrophin and pregnancy-specific β1-glycoprotein as immunohistochemical markers for extravillous trophoblast in pregnancy and trophoblastic disease

Summary

PP19, a new placental tissue protein, has α1-β1 electrophoretic mobility, a molecular weight of 36 500 and 3.9% carbohydrate. To study immunocytochemical PP19 localization in extravillous trophoblast, we obtained formalin-fixed specimens from extravillous tubal pregnancy at gestational weeks (GW) 7–9 (12 blocks); four early intrauterine pregnancies at GW 7–13 (12 blocks); four late pregnancies at GW 28–38 complicated with intramural uterine myoma, placenta increta and abruptio placenta (8 blocks); four invasive complete moles (9 blocks); and seven primary and metastatic gestational choriocarcinomas (12 blocks). Immunohistochemical staining was done for PP19, pregnancy-specific β1-glycoprotein (SP1) and human chorionic gonadotrophin (hCG) using the indirect-labeled antibody method [purified PP19 (Lot no. 225/242) and antibody against PP19 (Lot no. 632ZA) prepared by H. Bohn, antibodies against hCG (Behringwerke, Marburg, FRG) and SP1 (Dakopatts, Copenhagen, Denmark)]. In both early and late intrauterine pregnancies, the extravillous syncytiotrophoblastic cell (XST) showed positive staining for hCG and SP1 in the cytoplasm, as well as for PP19, which stained more intensively in the nucleus than in the cytoplasm. The three proteins were not seen in the evtravillous cytotrophoblastic cell (XCT) in the trophoblastic cell column and shell. The interstitial cytotrophoblast-like cell (ICT), which infiltrated into the decidua and myometrium, and their blood vessels, was immunoreactively positive for PP19 but negative for hCG and SP1 with the exception of SP1-positive ICT in the myometrium in late pregnancy. XST and ICT in the endosalpinx of tubal pregnancy stained for all three proteins. In invasive complete mole, XST stained for the three proteins, but ICT infiltrating into the decidua and myometrium stained more intensively for PP19 than for either hCG or SP1. XCT did not stain for the three proteins. Staining for the three proteins in gestational choriocarcinoma resembled that in invasive mole. By PP19 staining, XST and ICT infiltrating into surrounding tissue were clearly distinguishable from other cells of similar shape. PP19 staining thus can be a useful histochemical marker in assessing the cell viability of the trophoblastic tumor after chemotherapy.