A viral subunit immunogen for porcine transmissible gastroenteritis.

An immunogenic component was isolated from both the Illinois (propagated in young swine) and the Miller (cell culture-adapted) strains of porcine transmissible gastroenteritis (TGE) virus. The viral subunit was released from the virion by sonication and was separated from intact virus and other viral components by isopycnic centrifugation. It had a buoyant density in sucrose of 1.02 g/ml. Further purification consisted of gel filtration through Sephadex G200, in which process the immunogen, with a molecular weight of approximately 25 000, was the last component to be eluted. A group of ten young, weaned swine, inoculated intramuscularly with two or three 1-mg doses of the viral subunit were protected against challenge with virulent TGE virus, probably by the induction of secretory IgA. The immunogen also induced a humoral immune response of variable magnitude (titers ranging from 8 to 5 625) in the animals. These antibodies are not believed to be directly related to protection against infection. They can, however, be easily identified by serologic procedures and may serve as a convenient indicator of responsiveness to the TGE viral immunogen.