Pregnancy-associated major basic protein: deposition of protein and expression of mRNA at the maternal-fetal junction in early and late gestation.

Pregnancy-associated major basic protein (pMBP) has previously been isolated from human placenta and localized to the X cell. Here we used immunofluorescence staining and in situ hybridization to determine the distribution of pMBP and pMBP mRNA throughout the maternal-fetal junction in both early gestation tissues and at term. In early gestation tissues, pMBP was present only at the placental insertion site. Specifically, pMBP was present in (a) the decidua basalis (in the extracellular space, in interstitial pools and inside endometrial glands) and (b) intracellularly within extravillous interstitial trophoblasts in the decidua, in the myometrium and surrounding but not within luminal cells of spiral arteries. At term, the placental bed showed intense extracellular pMBP staining with little intracellular pMBP. In situ hybridization showed the presence of pMBP mRNA in both the early and late gestational tissues. pMBP mRNA was present in cells in the decidua, at the decidual-myometrial junction and in cell islands. Quantitative image analysis showed statistically significant hybridization signals with the pMBP antisense probe as compared to the control/sense probe. These results indicate that pMBP mRNA is expressed and pMBP is extensively deposited at the maternal-fetal junction in early pregnancy and at term.