Pregnancy in type I interferon receptor (IFNAR2) knockout sheep challenges the accepted paradigm for pregnancy recognition in ruminants

The effects of type I interferons, including interferon tau (IFNT), previously thought to be the signal for pregnancy recognition in ruminants, are mediated by the type I interferon receptor (IFNAR), a heterodimer comprised of IFNAR1 and IFNAR2. The genes encoding IFNAR were disrupted in fetal fibroblast cells using CRISPR/Cas9 and lambs were produced by somatic cell nuclear transfer (SCNT). Subsequently, a herd of IFNAR2+/- sheep was developed and used to produce IFNAR2-/- lambs. Functional knockout of IFNAR was confirmed by failure of fibroblast cell lines from IFNAR2-/- sheep to respond to interferon alpha or IFNT in a quantitative reverse-transcription polymerase chain reaction assay for interferon-stimulated gene expression. Wild-type cells respond robustly in this assay. Successful production of IFNAR2-/- lambs by SCNT demonstrated that the conceptus did not need to express IFNAR or respond to IFNT. Nevertheless, because the accepted paradigm suggested that IFNT was required for pregnancy recognition, we hypothesized that IFNAR2-/- ewes would be infertile. It was, therefore, surprising when two ~9-month-old IFNAR2-/- ewes bred to an IFNAR2+/- ram became pregnant and had normal pregnancies culminating in healthy lambs in May 2023. These pregnancies demonstrate that the IFNAR, and presumably IFNT, are not required for the establishment or normal progression of pregnancy. Since IFNAR-/- fetuses survive to term, and both IFNAR2-/- rams and ewes are fertile, unless there is another receptor for IFNT, which is unlikely, IFNT is not required for pregnancy recognition or the development of a healthy ruminant fetus.