MicroRNA Expression Profiling in Tonsils of Calves Challenged with a Laboratory Strain or Field Isolates of Bovine Respiratory Syncytial Virus

Bovine respiratory syncytial virus (BRSV) is a leading cause of bovine respiratory disease in cattle worldwide. MicroRNAs have been suggested to play a role in viral infections via their regulation of cellular molecules involved in either viral replication or in host innate immunity to infection. The objective of this study was to examine microRNA expression in tonsils of calves following BRSV challenge. Eight two-month old Holstein calves were randomly assigned to 4 groups: controls (n= 2), a group challenged with BRSV laboratory strain 375 (n= 2), a group challenged with field isolate 22301 (n= 2), or a group challenged with field isolate 33365 (n= 2).  Palatine tonsils were collected at day 7 post-infection, total RNA extracted, and RNA samples subjected to high throughput sequencing.  Compared to the controls, calves challenged with strain 375 had differential expression (P< 0.01) of two microRNAs (bta-mir-34c and bta-mir-215), while the groups challenged with field isolates 22301 and 33365 had differential expression (P < 0.01) of 11 and 13 microRNAs, respectively. Of these microRNAs, six were the same in both groups and showed similar trend in expression (bta-mir-136, bta-mir-154c, bta-mir-493, bta-mir-379, and bta-mir-450b were up-regulated, and bta-mir-15b was down-regulated). MicroRNAs induced by field isolates were mostly clustered on bovine chromosome 21. Field isolates exhibited a differential expression of a larger number of microRNAs when compared to calves challenged with strain 375. Further studies will be needed to establish the potential involvement of the identified microRNAs in innate immune response to BRSV.