Establishment of a specific radioimmunoassay for bovine interferon τ

A radioimmunoassay (RIA) was developed for quantification of bovine interferon (bIFN) τ, conceptus secretory protein, which allows for the maintenance of the corpus luteum during early pregnancy. A cDNA coding bIFNτ was derived from cultured trophoblast cells (TBs). Recombinant (r) bIFNτ was produced in a baculovirus expression system with two different viruses. The RIA was a double-antibody competitive binding assay that used anti-bIFNτ antiserum (raised in rabbits) as the primary antibody, a radioiodinated derivative of bIFNτ as the radioactive tracer, and goat anti-rabbit IgG as the secondary antibody. The antibody did not cross-react with rbIFNα, recombinant human IFNβ or recombinant ovine IFNτ. The correct recovery of amounts of rbIFNτ indicated good accuracy. Serially concentrated TB conditioned media, paralleled the standard curve for bIFNτ. The intra-assay and inter-assay coefficients of variation at bIFNτ levels of 7.8 and 15.6 ng/mL were 7.1 and 8.1%, and 11.0 and 8.5%, respectively. bIFNτ was directly detected in uterine flushings obtained from cows at Day 16 of pregnancy. In summary, this assay was suitable for the measurement of bIFNτ.