Francisella tularensis influences several host molecular/signaling pathways during infection. Ubiquitination and deubiquitination are among the most important regulatory mechanisms and respectively occur through attachment or removal of the ubiquitin molecule. The process is necessary not only to mark molecules for degradation, but also, for example, to the activation of signaling pathways leading to pro-inflammatory host response. Many intracellular pathogens, including Francisella tularensis, have evolved mechanisms of modifying such host immune responses to escape degradation. Here, we describe that F. tularensis interferes with the host's ubiquitination system. We show increased total activity of deubiquitinating enzymes (DUBs) in human macrophages after infection, while confirm reduced enzymatic activities of two specific DUBs (USP10 and UCH-L5), and demonstrate increased activity of USP25. We further reveal the enrichment of these three enzymes in exosomes derived from F. tularensis-infected cells. The obtained results show the regulatory effect on ubiquitination mechanism in macrophages during F. tularensis infection.

• Keywords
• DUBs, Francisella, UCH-L5, USP10, USP25, deubiquitination, exosomes, extracellular vesicles,
• MeSH
• Deubiquitinating Enzymes metabolism   MeSH
• Francisella tularensis * MeSH
• Gram-Negative Bacterial Infections * metabolism   MeSH
• Humans MeSH
• Macrophages MeSH
• Signal Transduction MeSH
• Ubiquitin Thiolesterase metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Deubiquitinating Enzymes MeSH
• Ubiquitin Thiolesterase MeSH
• USP10 protein, human MeSH Browser
• USP25 protein, human MeSH Browser

There remains to this day a great gap in understanding as to the role of B cells and their products-antibodies and cytokines-in mediating the protective response to Francisella tularensis, a Gram-negative coccobacillus belonging to the group of facultative intracellular bacterial pathogens. We previously have demonstrated that Francisella interacts directly with peritoneal B-1a cells. Here, we demonstrate that, as early as 12 h postinfection, germ-free mice infected with Francisella tularensis produce infection-induced antibody clones reacting with Francisella tularensis proteins having orthologs or analogs in eukaryotic cells. Production of some individual clones was limited in time and was influenced by virulence of the Francisella strain used. The phylogenetically stabilized defense mechanism can utilize these early infection-induced antibodies both to recognize components of the invading pathogens and to eliminate molecular residues of infection-damaged self cells.

• MeSH
• B-Lymphocytes immunology   metabolism   MeSH
• Cytokines metabolism   MeSH
• Francisella tularensis pathogenicity   MeSH
• Disease Models, Animal MeSH
• Mice, Inbred BALB C MeSH
• Mice MeSH
• Tularemia immunology   microbiology   MeSH
• Antibody Formation MeSH
• Virulence MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cytokines MeSH

Primary interaction of an intracellular bacterium with its host cell is initiated by activation of multiple signaling pathways in response to bacterium recognition itself or as cellular responses to stress induced by the bacterium. The leading molecules in these processes are cell surface membrane receptors as well as cytosolic pattern recognition receptors recognizing pathogen-associated molecular patterns or damage-associated molecular patterns induced by the invading bacterium. In this review, we demonstrate possible sequences of events leading to recognition of Francisella tularensis, present findings on known mechanisms for manipulating cell responses to protect Francisella from being killed, and discuss newly published data from the perspective of early stages of host-pathogen interaction.

• Keywords
• Francisella tularensis, innate immune recognition, intracellular replication, phagocytosis, signaling pathways,
• MeSH
• Alarmins genetics   immunology   MeSH
• Bacterial Proteins genetics   immunology   MeSH
• Phagocytosis genetics   MeSH
• Francisella tularensis genetics   immunology   pathogenicity   MeSH
• Host-Pathogen Interactions genetics   immunology   MeSH
• Humans MeSH
• Macrophages immunology   microbiology   MeSH
• Pathogen-Associated Molecular Pattern Molecules immunology   metabolism   MeSH
• Immunity, Innate * MeSH
• Receptors, Cell Surface genetics   immunology   MeSH
• Receptors, Pattern Recognition genetics   immunology   MeSH
• Gene Expression Regulation MeSH
• Signal Transduction MeSH
• Tularemia genetics   immunology   microbiology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Alarmins MeSH
• Bacterial Proteins MeSH
• Pathogen-Associated Molecular Pattern Molecules MeSH
• Receptors, Cell Surface MeSH
• Receptors, Pattern Recognition MeSH

Francisella tularensis is capable to modulate immunobiological activities of the host cells. We focused on the expression of ICAM-1 (CD54) on J774.2 mouse macrophage cell line infected by F. tularensis live vaccine strain (LVS) in vitro as a putative marker of subsequent elimination of infection. J774.2 cell line cells were infected by F. tularensis LVS strain (multiplicity of infection, 1:100). Cell cultures were stimulated either 3 h before infection or 3 h after infection by either lipopolysaccharide (LPS) or interferon γ (IFN-γ). The expression of ICAM-1 was determined by flow cytometry 6 h after infection. The intensity of ICAM-1 expression after 6 h of J774.2 macrophage cells infection by F. tularensis is very sensitive indicator of the effective macrophages stimulation resulting in the elimination of F. tularensis infection. The mean fluorescence intensity MFI = 49.8 is set-up by our experiments as a reliable threshold of the effective elimination of F. tularensis experimental infection with 83.3% sensitivity and 96.7% specificity, respectively. Simultaneous stimulation of J774.2 macrophage cells by LPS and IFN-γ was essential to elicit the elimination of F. tularensis infection. The ICAM-1 expression determined by flow cytometry can be considered to be highly sensitive and specific approach to predict elimination of F. tularensis infection by J774.2 macrophages.

• MeSH
• Macrophage Activation * MeSH
• Cell Line MeSH
• Francisella tularensis immunology   MeSH
• Interferon-gamma immunology   MeSH
• Lipopolysaccharides immunology   MeSH
• Macrophages immunology   microbiology   MeSH
• Intercellular Adhesion Molecule-1 biosynthesis   MeSH
• Mice, Inbred BALB C MeSH
• Mice MeSH
• Flow Cytometry MeSH
• Tularemia immunology   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Interferon-gamma MeSH
• Lipopolysaccharides MeSH
• Intercellular Adhesion Molecule-1 MeSH

Mutual interactions were investigated between intracellular parasitic bacterium Francisella tularensis (F.t.; highly virulent bacterium responsible for tularemia, replicating within the host macrophages) and murine macrophage-like cell line J774. Recombinant murine lymphokine INF-gamma and/or LPS derived from E. coli were determined to stimulate in vitro antimicrobial activity of macrophage-like J774 cell line against the live vaccine strain (LVS) of F.t. through their ability to produce proinflammatory cytokines and chemokines. F.t. infection up-regulated IL-12 p40 production and down-regulated TNF-alpha production by stimulated macrophages; on the other hand, F.t. infection did not affect the production of IL-8, IL-6, MCP-5, and RANTES by stimulated macrophages. This showed that F.t. infection modulates the cytokine synthesis by J774 macrophage cell line.

• MeSH
• Cell Line MeSH
• Chemokines immunology   MeSH
• Cytokines immunology   MeSH
• Francisella tularensis immunology   MeSH
• Macrophages immunology   microbiology   MeSH
• Mice MeSH
• Tularemia immunology   microbiology   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chemokines MeSH
• Cytokines MeSH