Transcriptome profiling of peripheral blood mononuclear cells from highly susceptible adult cattle infected with a virulent strain of Babesia bovis.

BACKGROUND: Bovine babesiosis is a tick-borne disease that poses a significant economic threat to cattle industries in tropical and subtropical areas, and Babesia bovis is the most virulent causative agent of bovine babesiosis. This apicomplexan parasite infects erythrocytes of cattle, causing severe hemolytic disease, and animals that survive an acute infection become persistently infected for life. Adult cattle (> 1 year of age) are highly susceptible and often succumb to acute infection. Protective host immunity involves peripheral blood mononuclear cells (PBMCs) including monocytes, dendritic cells (DC), natural killer (NK), T cells, and B cells, all of which act to control the pathogen. Monocytes release the cytokines interleukin (IL)-1β and tumor necrosis factor (TNF) and nitric oxide, in addition to chemokines that attract immature DCs. NK cells release IL-12, IL-18, and interferon gamma (IFNγ). Mature DC migrate to secondary lymphoid tissues to present Babesia antigens to T cells. B cells will produce antibodies against Babesia. METHODS: In this study, we examined the transcriptional signatures of PBMCs from adult cattle (aged > 1.5 years) experimentally infected with the B. bovis virulent strain Vir-S74-T3Bo, during the acute phase of babesiosis, at 10 days post infection (dpi), using RNA Sequencing (RNA-Seq) technology. RESULTS: Transcriptional signatures evident during the acute phase of babesiosis were cytokines and chemokines, such as IL-0, TNF, IL-1B, IL-18, CSF1, CXCL10 and CXCL16; pattern recognition receptors, such as CD14, TLR and NOD2; complement components, such as C1R, C2, C3aR1, CFB, CFI and CFP; cell adhesion molecules, such as ICAM1/2 and SELL; and apoptosis markers, such as CASP, BAX and BAK. We identified 1766 upregulated and 1508 downregulated genes, with fold changes ranging from two- to 429-fold. We discuss our findings in the context of immune responses to acute disease as a mechanism for adult host survival, with a focus on the molecular functions and biological processes involved in the response to B. bovis infection. CONCLUSIONS: In this RNA-Seq analysis, we identified genes that are up- and downregulated in response to acute B. bovis infection. Gene expression of IL-10, along with that of the inflammatory cytokines IL-1β, TNFα and IL-18, suggests a non-protective response to B. bovis at 10 dpi. These results enhance our understanding of the molecular interactions between Babesia and the host immune system.