Effect of parainfluenza-3 virus challenge on cell-mediated immune function in parainfluenza-3 vaccinated and non-vaccinated calves.

A group of four conventional, colostrum-fed calves was vaccinated with live parainfluenza type 3 (PI-3) virus vaccine at 1 and 5 weeks of age. A group of four control calves was treated with cell culture medium at the same time. Two weeks after the second vaccination, both groups of calves were challenged with PI-3 virus by a combined respiratory route. Blood and nasal mucus samples were collected at intervals, and alveolar macrophages were recovered before and after challenge by bronchoalveolar lavage. The results demonstrated that clearance of virus, as indicated by presence of virus antigen was more rapid in previously vaccinated calves. Several alveolar macrophage functions were markedly reduced in all calves 5 to 7 days following virus challenge, although microbicidal activity was unaffected, compared to the controls. The production of neutrophil chemotactic factors by alveolar macrophages occurred more rapidly after virus challenge in the previously vaccinated calves and this correlated with a more rapid neutrophil influx into the lungs in these animals.