Interferon-alpha-producing cells are localized in gut-associated lymphoid tissues in transmissible gastroenteritis virus (TGEV) infected piglets

Transmissible gastroenteritis virus (TGEV) infection of piglets results in a very rapid and massive release of IFN-alpha in serum and secretions. The objective of this work was to characterize the IFN-alpha -producing cells ( IPC) in tissues of TGEV-infected piglets. Caesarean-derived colostrum-depri ved piglets were infected orally with the TGEV virulent Miller strain and I PC were characterized in situ by immunohistochemistry, using a rabbit anti- pig IFN-alpha antiserum. IPC were almost exclusively detected in intestinal tissues and mesenteric lymph nodes (MLN), as early as 6 h post inoculation (p.i.), with a peak at 12-18 h. They disappeared by 24 h. IPC were localiz ed between enterocytes in the small intestine epithelial layer, in the lami na propria, around the Peyer's patches and, at highest frequency, in MLN. V ery few IPC were present in the spleen and popliteal lymph nodes of infecte d piglets. Double immunohistochemical staining for IFN-alpha and leukocyte markers on MLN cryosections showed that IPC were mainly Swine Leukocyte Ant igen (SLA) class II positive, and were not stained by an anti-macrophage (S WC3a) MAb. In addition, double staining with anti-TGEV and anti-IFN-alpha M Abs showed that viral antigens were present in MLN, close to IPC. These res ults show for the first time the presence of IPC in gut mucosa and gut-asso ciated lymphoid tissues in response to an enteropathogenic virus. Moreover, this work shows that IFN-alpha released in serum is likely to originate al most exclusively from gut IPC triggered locally by viral antigens to produc e IFN-alpha, since there were very few IPC in spleen or peripheral lymph no des. MHC class II molecule expression by gut-associated IPC suggests that t hese cells may be the in vivo mucosal counterparts of the dendritic cells r ecently shown to produce IFN-alpha after in vitro viral induction.