Serum immunoglobulin A antibody response in swine infected with transmissible gastroenteritis virus, as determined by indirect immunoperoxidase antibody test.

Using an immunoperoxidase antibody test, the serum immunoglobulin (Ig) A antibody titer was determined in swine naturally infected with transmissible gastroenteritis (TGE; group A), swine inoculated orally with high-virulent TGE virus (group B), and swine inoculated IM (group C) or orally (group D) with low-virulent TGE virus. Studies were then made on the relationship between active immunity to TGE and the serum IgA antibody titer. In group A swine, serum IgA antibody and virus-neutralizing (VN) antibody were absent in the serum collected in the acute stage, but were detected from the serum collected in the convalescent stage. In group B swine, serum IgA antibody and VN antibody began to be detected on postinoculation day (PID) 7 and were still detectable on PID 100. In group C and D swine, VN antibody was detected, but serum IgA antibody was not. Swine were inoculated orally with high-virulent TGE virus and were challenge exposed orally with the same strain of virus on PID 18, 21, 80, and 120 (group E). None of group E swine manifested clinical signs of infection. Their serum IgA antibody titers ranged from 2 to 512 at the time of inoculation. Swine were inoculated IM with low-virulent TGE virus and intranasally with the same virus on PID 60 (group F). They were challenge exposed with the high-virulent strain of TGE virus on PID 140, 200, and 260 (80, 140, and 200 days after the 2nd inoculation). At the time of challenge exposure, IgA antibody was undetected in serum at a 1:2 dilution. All group F swine had severe diarrhea 3 to 4 days after inoculation. Many of them vomited at the same time. In these swine, villous atrophy was observed in the jejunal portion of the small intestine. The VN antibody titer of porcine serum obtained at the time of challenge exposure was higher than was that determined in the group E swine. Seemingly, serum IgA antibody titer determined by the immunoperoxidase antibody test may be an indicator of active immunity to TGE.