Characterization of immunoglobulin A antibody in serum of swine inoculated with transmissible gastroenteritis virus.

Sera and contents of the small intestine from swine inoculated with transmissible gastroenteritis (TGE) virus were examined for immunoglobulin (Ig) A antibody responses by the radioimmunoprecipitation test with antiporcine IgA serum. When swine were orally inoculated with virulent virus, IgA antibody activity was detected in the contents of the small intestine and in serum from postinoculation days 7 to 56. However, IgA antibody activity was not detected in the contents of the small intestine or serum in swine inoculated IM with attenuated virus. The Ig class of serum of swine inoculated with TGE virus was examined by gel filtration chromatography. When swine were orally inoculated with virulent virus, neutralizing antibody was always detected from both fractions of IgA and IgG Neutralizing antibody ws detected only from the IgG fraction in the serum of swine inoculated IM with attenuated virus. The molecular size of serum IgA antibody was determined by sucrose density gradient centrifugation. The titer of this antibody was the highest at a position between 10.9S- and 7S-marker protein. The antibody consisted almost exclusively of dimers. It appeared that serum IgA antibody always originated from the lymphoid tissue of the intestinal tract. This antibody was regarded as an indicator of active immunity of TGE virus.