Cytokine messenger RNA expression in calves vaccinated intranasally with modified-live bovine respiratory syncytial virus (BRSV) prior to BRSV challenge
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In order to investigate mechanisms of cellular immune responses in bovine respiratory syncytial virus (BRSV) infected and vaccinated calves, total RNA was isolated from various sites of 3 groups of calves: vaccinated with modified live (ML) BRSV intranassally (i.n.) followed by challenge (V/C); mock vaccinated followed by challenge (M/C); and mock challenge only (control). Expression of several cytokines was measured by reverse transcriptase-competitive-PCR (RT-cPCR). To normalize the amount of cytokine cDNA, HPRT was used as a housekeeping gene, and the ratio of HPRT cDNA/competitor was kept in the range of 0.6-1.5. Relative ratios were calculated by the formula: (cytokine cDNA/competitor) / (HPRT cDNA/competitor). Groups were compared with Kruskall-Wallis test and Dunn’s post test for statistical analysis. Tumor necrosis factor-alpha (TNF-a) was measured in cranial lung and bronchoalveolar lavage fluid cells. Similar results were seen in both sites. Increased levels were present in M/C vs. V/C, and there was no difference between V/C and control. Interleukin-4 (IL-4) and interferon-gamma (IFN-.) were measured in pharyngeal tonsil and tracheobronchial lymph node. Relatively increased IL-4 expression occurred in the pharyngeal tonsil in M/C calves, and relatively increased IFN-. expression occurred in the tracheobronchial lymph node in M/C calves. The results indicated a Th2 bias in pharyngeal tonsil and a Th1 bias in tracheobronchial lymph node in M/C which was diminished in V/C calves. Intranasal vaccination may have prevented disease following challenge in part through causing a more balanced cytokine response to challenge.