Pregnancy-specific protein B induces release of an alpha chemokine in bovine endometrium

Pregnancy-specific protein B (PSPB), is secreted from binucleate trophoblas t of the bovine conceptus as early as day 15 of pregnancy. The objective of this experiment was to determine if PSPB induced uterine proteins. PSPB wa s purified from day 120 cotyledons using antibody-based affinity chromatogr aphy. Endometrium from day 14 nonpregnant cows (n = 3) was prepared for exp lant (H-3-Leu added) culture. Radiolabeled proteins released into medium we re dialyzed, separated using ID-PAGE, and detected using fluorography and d ensitometry. PSPB (0, 0.5, 5, 25 & 50 nM) caused a concentration-dependent increase in the release of a radiolabeled 8-kDa uterine protein. Western bl ots revealed that the 8-kDa protein cross-reacted with antibody against gra nulocyte chemotactic protein-2 (GCP-2). PSPB also induced release of GCP-2 by bovine endometrial (BEND) cells in primary culture. The induction of GCP -2 by PSPB was blocked by addition of antiserum against PSPB (1:4 molar rat io). This is the first indication that PSPB has a hormonal role in inducing GCP-2, an alpha chemokine that also is induced by interferon-tau during ea rly pregnancy. This chemotactic cytokine may be integral to mediating adhes ion, inflammation and angiogenesis associated with early implantation.