Abstract
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 calf), 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 respond 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.
Keywords: Bovine coronavirus, enteric disease, mucosal immunity, calf scours, regional immunity
Résumé
Une étude préliminaire a été réalisée pour comparer locale la réponse immunitaire au niveau intestinal de veaux nouveau-nés infectés par un coronavirus bovin virulent ou atténué et pour déterminer les causes d'échec des vaccinations. Un groupe de neuf veaux nouveau-nés, privés de colostrum, a été utilisé: deux veaux ont été infectés par un virus atténué, quatre par un virus virulent (incluant un veau naturellement infecté), et trois non infectés servirent de témoins. Les veaux inoculés par le virus virulent ont produit un titre en anticorps BCV plus important au niveau de l'intestin que ceux inoculés par le virus atténué. La différence de réponse chez les veaux inoculés par le virus atténué semble due à l'impossibilité du virus de se répliquer à des hauts titres. Le colon spiral, l'ileum et le jejunum ont prśentés une réponse immunologique différente; les plus hauts titres d'anticorps étaient trouvées dans le colon spiral, site primaire de l'infection et impliquaient quatre isotypes d'immunoglobulines bovines. La réponse immunitaire était plus faible dans l'lileum que dans le colon spiral. Elle s'est développée lentement dans le jejenum et était associée primitivement à des sous types d'immunoglobulines G.
Mots-clé: Coronavirus bovin, maladie enterifique, immunité des muqueuss, maladies du veau, immunité locale
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