PROBLEM: The endometrium of the sheep produces a progesterone-induced member of the serpin superfamily of serine proteinase inhibitors that can inhibit lymphocyte proliferation and reduce natural killer cell activity. Present results indicate that this molecule, called ovine uterine serpin (OvUS), can bind specifically to lymphocytes.
METHOD OF STUDY/RESULTS: Biotinylated OvUS bound to peripheral blood lymphocytes in a dose-dependent and saturable manner. Binding was inhibited by OvUS, but not by several other proteins, including serpin-enzyme complex (α1-antitrypsin-trypsin). Heparin blocked binding when added to the binding reaction or when used to pretreat lymphocytes. Both lymphocytes and Madin-Darby bovine kidney (MDBK) cells also bound fluorescein isothiocyanate-labeled OvUS.
CONCLUSIONS: Results suggest that OvUS can interact with lymphocytes and other cells through binding to a cell surface molecule. Such binding may indicate that inhibition of lymphocyte activation by OvUS involves 1) binding of OvUS to a cell surface receptor or 2) competitive inhibition of binding between OvUS and a co-activation molecule required for lymphocyte activation.