In vivo study of interferon-alpha-secreting cells in pig foetal lymphohaematopoietic organs following in utero TGEV coronavirus injection

Non-infectious UV-inactivated transmissible gastroenteritis virus (TGEV) was previously shown to induce interferon alpha (IFIMα) secretion following in vitro incubation with blood mononuclear cells. In this study, pig foetuses at different stages of gestation were injected in utero with (a) partially UV-inactivated wild TGEV or (b) fully UV-inactivated wild or dm49-4 mutant TGEV Coronavirus. Nucleated cells from foetal liver, bone marrow, spleen and blood were isolated 10 or 20 h after injection and assayed ex vivo for IFNα secretion by ELISPOT and ELISA techniques. The administration of TGEV induced IFNα-secreting cells in foetal lymphohaematopoietic organs at mid-gestation. In contrast, IFNα was not detected in control sham-operated foetuses. A specific point mutation in the amino acid sequence of the viral membrane glycoprotein M of TGEV mutant dm49-4 was associated with lower or absent IFNα in utero inducibility by mutant virus as compared with wild virus. Row cytometry analysis did not show differences in leukocyte surface marker expression between control and TGEV- or between dm49-4 and wild virus-treated foetus cells, with the exception of a reduction in percentages of polymorphonuclear cells in TGEV-treated lymphohaematopoietic tissues, which is probably due to IFNα secretion. The present data provided in vivo evidence of IFNα secretion at the cell level in foetal lymphohaematopoietic organs. Such IFNα-secreting cells in lymphohaematopoietic tissues may be the source of IFNα detected during foetal infections.