Reconstituted coronavirus TGEV virosomes lose the virus ability to induce porcine interferon-alpha production.

Riffault, S; Grosclaude, J; Vayssier, M; Laude, H; Charley, B

The transmissible gastroenteritis virus (TGEV) is a coronavirus which induces a strong interferon-alpha (IFN-alpha) production in vivo and in vitro. Previous studies have shown that the TGEV external protein M plays a major role in IFN-alpha induction by a non-infectious virus, whereas protein S is not involved. The present study extended these results by showing that monoclonal antibodies (MAbs) directed at the external viral protein sM could not block IFN-alpha induction, which argues against a direct role for this protein. In the same type of blocking experiment, MAbs to the TGEV receptor aminopeptidase N did not inhibit IFN-alpha induction, which strongly indicates that viral replication or entry through the receptor is not needed for TGEV induction of IFN-alpha in leukocytes. In an attempt to isolate functional envelope proteins, TGEV virions were detergent-solubilized and reconstituted in virosomes. Although BIAcore antigenic analysis revealed that the three external viral proteins were present on the virosomes, these proteins were unable to induce IFN-alpha in porcine leukocytes, and seemed to compete with the native virus for IFN-alpha induction. These data indicated that IFN-alpha inducing interactions between TGEV external proteins and leukocytes required a complex native envelope protein structure which has been lost in the virosomes.