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The many faces of macrophages : polarization, endotoxin priming, and Salmonella resistance

University of British Columbia

Different forms of macrophage activation or polarization are relevant in the pathogenesis of a variety of diseases from inflammatory conditions to infections. It has been previously established that classically activated or M1 macrophages such as those produced by IFNγ stimulation are non-permissive for intracellular Salmonella infection, while alternatively activated or M2 macrophages such as those produced by IL-4 stimulation are permissive for Salmonella growth. It is not known whether endotoxin tolerant macrophages (primed with endotoxin stimulation), such as those observed in sepsis, are permissive for Salmonella growth. A gentamicin protection assay was performed for these three types of differently polarized human monocyte-derived macrophages (MDM) in vitro, and bacterial load measured through colony counts and microscopy. Endotoxin primed MDM (MEP) had a similar bacterial load to M1 macrophages at the initial and 2-hour time-points, but became more susceptible to Salmonella by the 4- and 24-hour time-points. Transcriptomic comparisons using RNA-Seq were performed to generate hypotheses regarding mechanisms for the differences observed between these polarization types, based on differential gene expression. Key immune pathways including JAK-STAT were enriched in uninfected M1 and MEP compared to uninfected M2 macrophages, suggesting a priming effect on these pathways due to polarization. Meanwhile, Salmonella-infected M1 showed increased expression of key inflammasome genes and Salmonella resistance genes compared to M2 and MEP macrophages. These effects were also observed in similarly treated human induced-pluripotent stem cell derived macrophages (iPSDM), further validating the usefulness of iPSDM as a macrophage model in polarization and infection experiments. In order to investigate the mechanistic relevance of these observations, Ruxolitinib was applied to inhibit JAK1-2 during the polarization phase of the experiment. This increased Salmonella permissiveness at the 4-hour time point in resistant M1 macrophages, but not in M2 or MEP macrophages, which are susceptible at this time point. This is consistent with an important role for JAK-STAT priming and resistance to Salmonella infection. These observations provide insights into the effects of polarization on Salmonella resistance in macrophages, and the suitability of iPSDM for macrophage study.

Text

2020-04-27

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/74183

Microbiology and Immunology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/