Host- and genotype-specific transcriptomic responses to Mycoplasma bovis infection in bison and Holstein peripheral blood mononuclear cells.

The bacterial pathogen Mycoplasma bovis (M. bovis) emerged as the etiologic agent of mastitis in cattle during the early 1960's. Concurrent with the emergence of M. bovis, Holsteins in the US were undergoing intensive genetic selection for increased milk production. Comparison studies with unselected Holsteins have found an association with selection and increased susceptibility to disease. More recently, M. bovis was identified as the cause of epizootics of severe, chronic respiratory disease in American bison (Bison bison). In cattle, M. bovis causes chronic respiratory disease and is associated with the bovine respiratory disease complex while in bison, M. bovis is considered a primary pathogen. The objective of this study was to characterize and compare the transcriptomic response of peripheral blood mononuclear cells (PBMCs) from contemporary Holsteins (CH), unselected Holsteins (UH), and bison at 24 hr following in vitro M. bovis infection. The greatest and fewest number of differentially expressed genes (DEG) were observed in UH and bison, respectively. Ingenuity pathway analysis of DEG identified the genotype-specific expression of pathways involved in cytokine and chemokine response, neutrophil degranulation, and antigen processing and presentation. This study is the first to characterize how PBMC transcriptomic responses to in vitro M. bovis infection differ by genotype (CH vs. UH) and species (Holstein vs. bison). These findings provide insight into observed differences in clinical disease between bison and cattle and highlight the effects of primary selection for milk production on Holstein responses to M. bovis.