ANTIBODY-RESPONSES IN SPIRAL COLON, ILEUM, AND JEJUNUM OF BOVINE CORONAVIRUS-INFECTED NEONATAL CALVES

A preliminary study was conducted to compare the regional intestinal i mmune responses of neonatal calves inoculated with virulent or attenua ted bovine coronavirus (BCV) to determine the cause of reported vaccin e failures. A group of 9 newborn, colostrum-deprived calves was used; two calves were inoculated with attenuated virus, four calves were inf ected with virulent virus (including one naturally infected calf), and three calves were uninfected controls. Calves inoculated with virulen t virus produced higher titers of BCV antibodies in the intestines tha n those inoculated with the attenuated virus. The failure of the calve s to respond to the attenuated virus was apparently due to the inabili ty of the virus to replicate to high titers. Spiral colon, ileum, and jejunum were found to be immunologically distinct; the highest anti-BC V antibody responses were detected in spiral colon, the primary site o f infection, and involved all four isotypes of bovine immunoglobulins. The antibody response in ileum was lower than in spiral colon. The im mune responses developed slowly in jejunum and were associated primari ly with the IgG subtypes.