Immunoreactivity with S100 protein as an indicator of pregnancy.

The usefulness as a pregnancy marker, of immunoreactivity with S100 protein antiserum in endometrial curettings and fallopian tubes during pregnancy was assessed. Twenty six placental tissues of various gestational age, two hydatidiform moles and four fallopian tubes removed for ectopic pregnancy were stained with S100 protein polyclonal antiserum by immunoperoxidase technique. Strong immunostaining was found in glands within the decidua and epithelial cells of fallopian tubes during early pregnancy. However, no S100 protein could be demonstrated in the endometrium in various phases, endometrial carcinomas, decidual glands beyond 12 wk of gestation and normal fallopian tubes. The results indicate a relationship between S100 protein and early pregnancy. Positive immunoreactivity with S100 protein antiserum in the decidual glands and fallopian tube epithelium may help in confirmation of doubtful cases of pregnancy.