Characteristics of pregnancy-specific protein B in cattle.

Pregnancy-specific protein B (PSPB) has been isolated from placental tissue of cows. Antisera were developed against PSPB and by immunohistochemical techniques the protein was localized to the binucleated cells of the trophoblastic ectoderm. A radioimmunoassay (RIA) was also developed and used to detect PSPB in sera of pregnant animals. The RIA has been used successfully in pregnancy testing in cattle and other ruminants. The assay can also be used to detect time of embryonic death. Chemical characterization of PSPB showed that it was an acidic glycoprotein with an apparent molecular weight of 78,000. It has several isoelectric variants with pIs of 4.0-4.4.