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Interferon‐gamma gene and protein are spontaneously expressed by the porcine trophectoderm early in gestation

The nature and the source of the antiviral activity found in the reproductive tract of pregnant gilts early in gestation were analyzed. Two antigenically distinct antiviral activities were found in uterine flushings and in supernatants of conceptus‐conditioned culture medium between days 12 and 20 of gestation, using Madin Darby bovine kidney cells and vesicular stomatitis virus as a challenge in the antiviral bioassay. One component was antigenically identified as interferon‐γ (IFN‐γ). Northern blot analysis of conceptus poly(A)+ RNA with a human IFN‐γ cDNA probe revealed two mRNA of 1.3 and 1.4 kb. In addition, immunoprecipitation of metabolically labeled conceptus secretory proteins with an antiserum raised against purified porcine rIFN‐γ resulted in four bands in sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, with molecular mass 18.5 to 24.5 kDa. Pre‐electrophoresis incubation of the immunoprecipitate with glycopeptidase F, which removes N‐linked carbohydrates, yielded a single band of 16.5 kDa. Finally, staining of ultrathin sections by indirect immunofluorescence using the same antiserum to rIFN‐γ revealed that all cells of extra‐embryonic trophectoderm contained intensely fluorescent granules in their apical cytoplasm. Neither endoderm nor embryonic cells stained positive. These results clearly show that IFN‐γ, known so far as a T or NK cell‐derived lymphokine, is spontaneously and intensively secreted by the porcine trophectoderm, an embryonic tissue not related to the hematopoietic lineage. They also suggest that the implanting conceptus, at least in the porcine species, could play an active role in immune interactions with the mother.