Antibody responses in spiral colon, ileum, and jejunum of bovine coronavirus-infected neonatal calves.

A preliminary study was conducted to compare the regional intestinal immune responses of neonatal calves inoculated with virulent or attenuated bovine coronavirus (BCV) to determine the cause of reported vaccine failures. A group of 9 newborn, colostrum-deprived calves was used; two calves were inoculated with attenuated virus, four calves were infected with virulent virus (including one naturally infected calve), and three calves were uninfected controls. Calves inoculated with virulent virus produced higher titers of BCV antibodies in the intestines than those inoculated with the attenuated virus. The failure of the calves to response to the attenuated virus was apparently due to the inability of the virus to replicate to high titers. Spiral colon, ileum, and jejunum were found to be immunologically distinct; the highest anti-BCV antibody responses were detected in spiral colon, the primary site of infection, and involved all four isotypes of bovine immunoglobulins. The antibody response in ileum was lower than in spiral colon. The immune responses developed slowly in jejunum and were associated primarily with the IgG subtypes.