SECRETION OF BIOLOGICALLY-ACTIVE INTERFERON-TAU BY IN-VITRO-DERIVED BOVINE TROPHOBLASTIC TISSUE

Secretion of interferon tau (IFN tau) by trophoblastic tissue has been shown to be the first embryonic signal for pregnancy recognition, The refore we tried to derive biologically active trophoblastic tissue by in vitro techniques. Since conventional in vitro conditions for bovine embryo development were not sufficient for long-term culture, we test ed more complex culture conditions, including Menezo B2 or Buffalo rat liver (BRL) cell-conditioned medium, for their ability to support pro liferation and IFN tau secretion by in vitro-derived trophoblastic tis sue. IFN tau activity was determined by using a biological assay based on the inhibition of the cytopathic effect of vesicular stomatitis vi rus on Madin-Darby bovine kidney cells. When cultures of individual ha tched blastocysts were started in 60-mu l drops of BRL cell-conditione d medium, mean IFN tau secretion (antiviral units/ml/48 h) corresponde d to 1200 on Day 11 and to 5000 on Day 13 (p < 0.01). To characterize trophoblast cell-specific secretions, the inner cell mass was removed from all embryos by microsurgery on Day 13. IFN tau secretion by troph oblastic tissue increased to mean levels of > 10(5) antiviral units/ml /48 h on Day 23, stayed high for about 1 wk, and then slowly declined to levels below 10(3) antiviral U/ml/48 h. The specificity of the cyto protective effect of IFN tau was tested by Western blot analysis and b y immunoneutralization with use of a polyclonal antiserum specific to IFN tau. Our results demonstrate that viable trophoblastic tissue can be maintained entirely in vitro and secretes high amounts of IFN tau.