IN-VIVO INDUCTION OF INTERFERON-ALPHA IN PIG BY NONINFECTIOUS CORONAVIRUS - TISSUE LOCALIZATION AND IN-SITU PHENOTYPIC CHARACTERIZATION OF INTERFERON-ALPHA-PRODUCING CELLS

A low frequency peripheral blood mononuclear cell (PBMC) subpopulation , referred to as natural interferon-producing (NIP) cells, is describe d as producing interferon-alpha (IFN-alpha) following contact with non -infectious viral structures, namely viral glycoproteins, These cells are characterized in vitro as non-T, non-B, MHC class II+ and CD4(+) c ells, In this study, NIP cells were analysed in vivo after an intraven ous injection of UV-inactivated transmissible gastroenteritis virus in newborn piglets, which resulted in strong serum IFN-alpha production. Splenocytes, but not PBMC, were the IFN-alpha producers in vivo. Usin g double immunohistochemical labelling for both IFN-alpha and leukocyt e markers, we established that splenic NIP cells were not T or B cells . The majority were MHC class II+ and only a minority expressed a macr ophage marker. NIP cells were localized in contact with MHC class tl-e xpressing cells and T cells, which suggested that NIP cells might modu late the antiviral immune response.