Identification of ovine interferons: differential activities derived from fibroblast and lymphoid cells

A bioassay has been developed to detect interferon (IFN) activity in supernatant fluids of cultured sheep cells by measuring their ability to inhibit the cytopathic effect of Semliki Forest Virus on an immortalised ovine fibroblastic cell line. IFN produced by spleen or lymph node cells stimulated with mitogen was labile at pH 2 as was a similar activity produced by CD4 lymphocytes stimulated with mitogen or specific antigen. In contrast, the IFN produced by fibroblasts stimulated with synthetic double-stranded RNA was stable at that pH. These results demonstrate the existence of an ovine IFN with properties similar to those described for IFN-gamma in mouse and man.