Burkholderia sp. modulation of host immune response genes and pathways:
Aschenbroich, Sophie Ann
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Among the Burkholderia genus, Burkholderia mallei (Bm) and Burkholderia pseudomallei (Bp) represent pathogens capable of causing fatal infections in animals and humans. Disease manifestations range from acute septicemia to chronic infection, wherein the facultative intracellular behavior of these agents promotes long-term persistence within host tissues. This ability to thrive intracellularly is thought to be related to exploitation of host immune response genes and pathways. As compared to Bp, less is known regarding the molecular strategies employed by Bm to modulate host immune responses and evade intracellular killing. To fill the gaps in our understanding of the interface between Bm and host immune cells as part of the effort to develop effective countermeasures, we designed an intracellular survival assay with human Mono Mac-6 (Mm6) monocytes and profiled the transcriptome of Bm- infected monocytes on a genome-wide scale. Gene expression changes in Bm-infected monocytes were compared to those of monocytes infected with the relatively non-pathogenic, genetically-related, Burkholderia thailandensis (Bt) and to uninfected monocytes. Negative regulators of inflammation, IL-17 signaling, and Pattern Recognition Receptor (PRR) pathways were represented among significantly modulated genes and pathways in infected monocytes. To investigate the role of negative regulators of inflammation in the pathogenesis of Bm, we developed a nucleofection system for gene silencing in Mm6 monocytes and explored functional inhibition studies. Our efforts to define interactions between Bm and IL-17 signaling during intracellular infection also led us to evaluate the potential priming effects of IL-17A stimulation on Mm6 monocytes. While the role of negative regulators of inflammation and IL- 17 signaling in Bm infection could not be conclusively elucidated, this research provides a novel understanding of the relationship between components of innate immunity induced during infection, such as soluble PRRs, and Burkholderia sp. Following the upregulation of the soluble PRR, pentraxin-3 (PTX3), by Bm- and Bt-infected monocytes, we report on PTX3 as a novel opsonin of Bt and Bp, together with the evasion of PTX3 recognition by Bm. While studies with Bt did not suggest a role for PTX3 in potentiating complement-mediated lysis, opsonophagocytosis, or replication within monocytes, the role of PTX3 in Bm pathogenesis remains to be clarified.