Studies on pathogen-host interaction: Impact of the emerging zoonotic pathogen Arcobacter butzleri on human macrophages

Cases of severe gastroenteritis caused by the new emerging pathogen A. butzleri have been recently reported but data to evaluate the pathogenic potential is sparse. Expanding the knowledge of the interplay between A. butzleri and its host is indispensable to evaluate the pathogenicity and to develop strategies to combat A. butzleri induced diseases. Macrophages have a fundamental role in the first line of host defense and were therefore matter of investigation. The first part of this work focused on the inflammatory response of macrophages as well as intracellular survival and modulation of host cell apoptosis as potential virulence mechanisms employed by A. butzleri. THP-1 cell derived macrophages were used as an in vitro infection model. Induction of IL-1α, IL-1β, IL-6, IL-8, IL-12β and TNFα demonstrated a proinflammatory response of infected macrophages towards A. butzleri. Gentamycin protection assays revealed the ability of the pathogen to survive and resist the hostile environment of phagocytic immune cells for up to 22 h and apoptosis assays proved the initial induction of adapter- as well as effector caspases which was not followed by DNA damage, suggesting a possible counter regulation. A potential role of miR-106a in this context could not be demonstrated. The considered investigations demonstrate that A. butzleri employs virulence mechanisms to attenuate host defense similar to those used by other severe intestinal pathogens such as Campylobacter jejuni. Additionally, distinct isolate-dependent differences were observed among the strains suggesting the existence of strain-specific phenotype variations possibly exhibiting different virulent potential. The second part of this work concentrated on the role of miRNAs upon Arcobacter infection. The infection of primary human macrophages of three different donors with A. butzleri and subsequent miRNAseq contributed new data to understand the regulatory network of miRNAs expressed during bacterial infection. Analysis of the data revealed the expression of miR-125a, miR-146a, miR-155, miR-212, miR-181b/c/d, miR-21, miR-99b, miR-27a, let-7a, miR-26b and miR-148a. These miRNAs have been reported to be mainly involved in the autoregulative control of a balanced immune response during infectious diseases. Additionally, miRNAs which have not yet been reported to be involved in infectious diseases were expressed in A. butzleri infected macrophages (miR-3613, miR-590, miR-941, miR-2116, miR-671, miR-30d, miR-339, miR-629 and miR-193a). Taken together, the data generated in this study contributes new findings to the existing knowledge about the interplay of the new emerging pathogen A. butzleri with human host cells which is necessary to evaluate the severeness of the disease and develop appropriate therapeutics.