Glycosylation is required for coronavirus TGEV to induce an efficient production of IFN alpha by blood mononuclear cells.
Porcine peripheral blood mononuclear cells (PBMC) are induced to produce interferon alpha (IFN alpha) following in vitro exposure to coronavirus TGEV (transmissible gastroenteritis virus)-infected glutaraldehyde-fixed cell monolayers or to TGEV virions. In the present report, we examined the possibility that glycosylation of viral proteins could play a major role in interactions with PBMC leading to the production of IFN alpha. Con A pretreatment of TGEV-infected cell monolayers before fixation with glutaraldehyde and exposure to PBMC caused a dose-dependent inhibition of IFN alpha induction, implying that masking of carbohydrates at the surface of infected cells lowered IFN-alpha-induction. Similarly, inhibition of N-linked glycosylation by tunicamycin during viral infection of cell monolayers altered their ability to induce IFN alpha. In addition, complete cleavage of 'complex type' oligosaccharides by peptide-N-glycohydrolase F lowered the capacity of TGEV virions to induce IFN alpha. Thus, these findings strongly suggest that glycosylation of the viral proteins, and more precisely the presence of complex-type oligosaccharides, is an important requirement for a completely efficient interaction with PBMC leading to the production of IFN-alpha.