Transcriptional analyses identify genes that modulate bovine macrophage response to Toxoplasma infection and immune stimulation

The obligate intracellular parasite, Toxoplasma gondii, is highly prevalent among livestock species. Although cattle are generally
resistant to Toxoplasma strains circulating in Europe and North America, the underlying mechanisms are largely unknown. Here,
we report that bovine bone marrow‐derived macrophage (BMDM) pre‐stimulated with interferon gamma (IFNγ) restricts
intracellular Toxoplasma growth independently of nitric oxide. While Toxoplasma promoted the expression of genes associated
with alternative macrophage activation and lipid metabolism, IFNγ abrogated parasite‐induced transcriptional responses and
promoted the expression of genes linked to the classical macrophage activation phenotype. Additionally, several chemokines, including CCL22, that are linked to parasite‐induced activation of the Wnt/‐catenin signaling were highly expressed in
Toxoplasma‐exposed naïve BMDMs. A chemical Wnt/‐catenin signaling pathway antagonist significantly reduced intracellular
parasite burden in naïve BMDMs, suggesting that Toxoplasma activates this pathway to evade bovine macrophage anti-parasitic
responses. Congruently, intracellular burden of a mutant Toxoplasma strain (RHdeltaASP5) that does not secrete dense granule
proteins into the host cell, which is an essential requirement for parasite‐induced activation of the Wnt/‐catenin pathway, was
significantly reduced in naïve BMDMs. However, both the Wnt/‐catenin antagonist and RHASP5 did not abolish parasite burden
differences in naïve and IFNγ‐stimulated BMDMs. Finally, we observed that parasites infecting IFNγ‐stimulated BMDMs largely
express genes associated with the slow dividing bradyzoite stage. Overall, this study provides novel insights into bovine
macrophage transcriptional response to Toxoplasma. It establishes a foundation for a mechanistic analysis IFNγ‐induced bovine
anti-Toxoplasma responses and the counteracting Toxoplasma survival strate