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Innate Immun. 2018 Apr;24(3):152-162. doi: 10.1177/1753425918760180. Epub 2018 Feb 26.

Microbial co-infection alters macrophage polarization, phagosomal escape, and microbial killing.

Author information

1
1 Department of Biology, the South Texas Center for Emerging Infectious Diseases, and the Center for Excellence in Infection Genomics, University of Texas at San Antonio, USA.
2
2 The Heartland National TB Center at San Antonio, USA.
3
3 The Department of Microbiology, Immunology and Molecular Genetics, University of Kentucky, USA.

Abstract

Macrophages are important innate immune cells that respond to microbial insults. In response to multi-bacterial infection, the macrophage activation state may change upon exposure to nascent mediators, which results in different bacterial killing mechanism(s). In this study, we utilized two respiratory bacterial pathogens, Mycobacterium bovis (Bacillus Calmette Guẻrin, BCG) and Francisella tularensis live vaccine strain (LVS) with different phagocyte evasion mechanisms, as model microbes to assess the influence of initial bacterial infection on the macrophage response to secondary infection. Non-activated (M0) macrophages or activated M2-polarized cells (J774 cells transfected with the mouse IL-4 gene) were first infected with BCG for 24-48 h, subsequently challenged with LVS, and the results of inhibition of LVS replication in the macrophages was assessed. BCG infection in M0 macrophages activated TLR2-MyD88 and Mincle-CARD9 signaling pathways, stimulating nitric oxide (NO) production and enhanced killing of LVS. BCG infection had little effect on LVS escape from phagosomes into the cytosol in M0 macrophages. In contrast, M2-polarized macrophages exhibited enhanced endosomal acidification, as well as inhibiting LVS replication. Pre-infection with BCG did not induce NO production and thus did not further reduce LVS replication. This study provides a model for studies of the complexity of macrophage activation in response to multi-bacterial infection.

KEYWORDS:

BCG; Francisella; IL-4; co-infection; macrophage

PMID:
29482417
DOI:
10.1177/1753425918760180

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