IN-VIVO STUDY OF INTERFERON-ALPHA-SECRETING CELLS IN PIG FETAL LYMPHOHAEMATOPOIETIC ORGANS FOLLOWING IN-UTERO TGEV CORONAVIRUS INJECTION

Non-infectious UV-inactivated transmissible gastroenteritis virus (TGE V) was previously shown to induce interferon alpha (IFN alpha) secreti on 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-ina ctivated wild or dm49-4 mutant TGEV coronavirus. Nucleated cells from foetal liver, bone marrow, spleen and blood were isolated 10 or 20 h a fter injection and assayed ex vivo for IFN alpha secretion by ELISPOT and ELISA techniques. The administration of TGEV induced IFN alpha-sec reting cells in foetal lymphohaematopoietic organs at mid-gestation. I n contrast, IFN alpha was not detected in control sham-operated foetus es. A specific point mutation in the amino acid sequence of the viral membrane glycoprotein M of TGEV mutant dm49-4 was associated with lowe r or absent IFN alpha in utero inducibility by mutant virus as compare d with wild virus. Plow cytometry analysis did not show differences in leukocyte surface marker expression between control and TGEV- or betw een 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 IFN alpha secre tion. The present data provided in vivo evidence of IFN alpha secretio n at the cell level in foetal lymphohaematopoietic organs. Such IFN al pha-secreting cells in lymphohaemapoietic tissues may be the source of IFN alpha detected during foetal infections.