Non-infectious UV-inactivated transmissible gastroenteritis virus (TGEV) was previously shown to induce interferon alpha (IFN alpha) 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 IFN alpha secretion by ELISPOT and ELISA techniques. The administration of TGEV induced IFN alpha-secreting cells in foetal lymphohaematopoietic organs at mid-gestation. In contrast, IFN alpha 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 IFN alpha in utero inducibility by mutant virus as compared with wild virus. Flow 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 IFN alpha secretion. The present data provided in vivo evidence of IFN alpha secretion at the cell level in foetal lymphohaematopoietic organs. Such IFN alpha-secreting cells in lymphohaematopoietic tissues may be the source of IFN alpha detected during foetal infections.

Nous avons montré précédemment que l’incubation in vitro de cellules mononucléées sanguines avec du Coronavirus de la gastroentérite transmissible (VGET) inactivé par irradiation UV, induisait la sécrétion d’interféron alpha (IFNα). Le travail présenté ici a consisté à réaliser sur des foetus de porcs à différents stades de gestation une injection in utero (a) de VGET sauvage partiellement inactivé par les UV, ou (b) de virus sauvage ou de mutant dm49-4 totalement inactivés. La sécrétion d’IFNα par les cellules nucléées isolées, 10 ou 20 h après injection, de la rate, du foie, de la moelle osseuse et du sang fœtaux a été analysée ex vivo par technique ELISPOT et ELISA. L’injection de VGET a induit la présence de cellules sécrétrices d’IFNα dans les organes lymphohématopoïétiques fœtaux à mi-gestation. Une sécrétion d’IFNα plus faible, voire absente, a été observée à la suite de l’injection du mutant viral dm49-4 caractérisé par une mutation ponctuelle dans la séquence de la glycoprotéine M. L’étude en cytometric de flux n'a pas permis de montrer de différences d’expression des marqueurs de surface leucocytaires entre les cellules de fœtus traités par le VGET ou par du milieu, ou traités par le virus sauvage ou le mutant dm49-4, à l’exception d’une réduction du pourcentage de polynucléaires, après injection par le VGET, probablement due à l’INFα sécrété. Ces résultats montrent, in vivo, la sécrétion au niveau unicellulaire d’IFNα dans les tissus lymphohématopoïétiques fœtaux. De telles cellules sécrétrices d’IFNα localisées dans les tissus pourraient constituer la source de l’IFNα qui est détecté au cours d’infections fœtales.

Division of Immunology and Gnotobiology Academy of Sciences of the Czech Republic Nový Hrádek

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