Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2003
Publication Date: 6/6/2004
Citation: Miao, C., Brown, C., Brown, J.C., Williams, S., Scott, M., Zarlenga, D.S., Woolums, A. 2003. Cytokine messenger RNA expression in calves vaccinated intranasally with modified-live bovine rspiratory syncytial virus (BRSV)prior to BRSV challenge. American Journal of Veterinary Research. 65(6):725-33. Interpretive Summary: Bovine respiratory syncytial virus (BRSV) causes substantial loss in milk production as well as extensive costs to the producer for labor and chemical treatment to the animals. Nationwide studies have shown that BRSV is present in 38% to 76% of beef and dairy herds. The virus can infect cattle of all ages; however, it has been identified as significantly more important in both nursing and weaned calves. Little is known of the immune response that is generated to this important pathogen. To this end, reagents developed at the USDA were used to assess changes in the immune status of infected and vaccinated animals. Results indicated that the elevation in TNF-alpha gene expression in the lung and bronchoalveolar lavage fluid is associated with the presence of BRSV and that vaccination resulted in decreased pulmonary inflammation. These results will assist in designing better vaccine candidates to prevent disease.
Technical Abstract: The development of safe and effective vaccines for bovine respiratory syncytial virus (BRSV) has been problematic, and T helper cell cytokine expression may be linked to outcome following vaccination. Intranasal (i.n.) vaccination may be safer and more effective than existing strategies, but the cytokine response to i.n. BRSV vaccination has not been studied. The objective of this study was to characterize cytokine mRNA expression in various sites of calves vaccinated once i.n. with modified live BRSV prior to challenge. Calves received live high passage BRSV i.n. (V/C, n=4) or mock vaccine i.n. (M/C, n=5) followed by challenge; a third group received only mock challenge (Control, n=3). Clinical signs were evaluated daily; calves were euthanized at day 7 post challenge. Total RNA was isolated from cranial lung, bronchoalveolar lavage fluid (BAL) cells, pharyngeal tonsil and tracheobronchial lymph node. Cytokine mRNA was quantified by reverse transcriptase-competitive PCR (RT-cPCR). Message for TNF-alpha was measured in lung and BAL cells; message for IL-4 and IFN-gamma was measured in pharyngeal tonsil and tracheobronchial lymph node. Vaccinated calves were protected from severe disease following challenge. TNF-alpha mRNA levels in cranial lung and BAL were higher in the M/C group than in the other two groups (p < 0.05). In the pharyngeal tonsil, IL-4 and IFN-gamma expression, and the ratio of IL-4/IFN-gamma expression, were significantly increased in the M/C group as compared to the Control group (p < 0.05) and was moderately higher relative to the V/C group. There were no differences between the Control and the V/C groups. In the tracheobronchial lymph node, there was no significant difference in IL-4 message expression or the ratio of IL-4/IFN-gamma expression between groups. Interferon gamma expression was significantly increased in the M/C group compared to the V/C group (p < 0.05); there was no significant difference in IFN-gamma message expression between the Control and V/C groups. Infection with BRSV induced pulmonary inflammation as evidenced by increased expression of message for TNF-alpha in the lung and BAL cells, and protection due to i.n. vaccination was associated with decreased inflammation. A Th2 bias in the response to BRSV infection, indicated by an increased ratio of IL-4/IFN- ¿ message expression, was present in the pharyngeal tonsil but not in the tracheobronchial lymph node. This bias was diminished in vaccinated calves. Intranasal BRSV vaccination protected calves from virulent challenge; protection was associated with changes in expression of relevant cytokines in the lung and regional lymphoid tissue.