Publications by authors named "Trung H M Pham"

7 Publications

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A Salmonella Typhi RNA thermosensor regulates virulence factors and innate immune evasion in response to host temperature.

PLoS Pathog 2021 Mar 2;17(3):e1009345. Epub 2021 Mar 2.

Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California, United States of America.

Sensing and responding to environmental signals is critical for bacterial pathogens to successfully infect and persist within hosts. Many bacterial pathogens sense temperature as an indication they have entered a new host and must alter their virulence factor expression to evade immune detection. Using secondary structure prediction, we identified an RNA thermosensor (RNAT) in the 5' untranslated region (UTR) of tviA encoded by the typhoid fever-causing bacterium Salmonella enterica serovar Typhi (S. Typhi). Importantly, tviA is a transcriptional regulator of the critical virulence factors Vi capsule, flagellin, and type III secretion system-1 expression. By introducing point mutations to alter the mRNA secondary structure, we demonstrate that the 5' UTR of tviA contains a functional RNAT using in vitro expression, structure probing, and ribosome binding methods. Mutational inhibition of the RNAT in S. Typhi causes aberrant virulence factor expression, leading to enhanced innate immune responses during infection. In conclusion, we show that S. Typhi regulates virulence factor expression through an RNAT in the 5' UTR of tviA. Our findings demonstrate that limiting inflammation through RNAT-dependent regulation in response to host body temperature is important for S. Typhi's "stealthy" pathogenesis.
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http://dx.doi.org/10.1371/journal.ppat.1009345DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7954313PMC
March 2021

Salmonella-Driven Polarization of Granuloma Macrophages Antagonizes TNF-Mediated Pathogen Restriction during Persistent Infection.

Cell Host Microbe 2020 01 26;27(1):54-67.e5. Epub 2019 Dec 26.

Department of Microbiology and Immunology, Stanford University, Stanford, CA, USA. Electronic address:

Many intracellular bacteria can establish chronic infection and persist in tissues within granulomas composed of macrophages. Granuloma macrophages exhibit heterogeneous polarization states, or phenotypes, that may be functionally distinct. Here, we elucidate a host-pathogen interaction that controls granuloma macrophage polarization and long-term pathogen persistence during Salmonella Typhimurium (STm) infection. We show that STm persists within splenic granulomas that are densely populated by CD11bCD11cLy6C macrophages. STm preferentially persists in granuloma macrophages reprogrammed to an M2 state, in part through the activity of the effector SteE, which contributes to the establishment of persistent infection. We demonstrate that tumor necrosis factor (TNF) signaling limits M2 granuloma macrophage polarization, thereby restricting STm persistence. TNF neutralization shifts granuloma macrophages toward an M2 state and increases bacterial persistence, and these effects are partially dependent on SteE activity. Thus, manipulating granuloma macrophage polarization represents a strategy for intracellular bacteria to overcome host restriction during persistent infection.
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http://dx.doi.org/10.1016/j.chom.2019.11.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065835PMC
January 2020

Salmonella Effector SteE Converts the Mammalian Serine/Threonine Kinase GSK3 into a Tyrosine Kinase to Direct Macrophage Polarization.

Cell Host Microbe 2020 01 17;27(1):41-53.e6. Epub 2019 Dec 17.

MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, UK. Electronic address:

Many Gram-negative bacterial pathogens antagonize anti-bacterial immunity through translocated effector proteins that inhibit pro-inflammatory signaling. In addition, the intracellular pathogen Salmonella enterica serovar Typhimurium initiates an anti-inflammatory transcriptional response in macrophages through its effector protein SteE. However, the target(s) and molecular mechanism of SteE remain unknown. Here, we demonstrate that SteE converts both the amino acid and substrate specificity of the host pleiotropic serine/threonine kinase GSK3. SteE itself is a substrate of GSK3, and phosphorylation of SteE is required for its activity. Remarkably, phosphorylated SteE then forces GSK3 to phosphorylate the non-canonical substrate signal transducer and activator of transcription 3 (STAT3) on tyrosine-705. This results in STAT3 activation, which along with GSK3 is required for SteE-mediated upregulation of the anti-inflammatory M2 macrophage marker interleukin-4Rα (IL-4Rα). Overall, the conversion of GSK3 to a tyrosine-directed kinase represents a tightly regulated event that enables a bacterial virulence protein to reprogram innate immune signaling and establish an anti-inflammatory environment.
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http://dx.doi.org/10.1016/j.chom.2019.11.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6953433PMC
January 2020

DOCK8 is essential for T-cell survival and the maintenance of CD8+ T-cell memory.

Eur J Immunol 2011 Dec 10;41(12):3423-35. Epub 2011 Nov 10.

Nuffield Department of Medicine, Henry Wellcome Building of Molecular Physiology, Oxford University, Oxford, UK.

Deficiency in the guanine nucleotide exchange factor dedicator of cytokinesis 8 (DOCK8) causes a human immunodeficiency syndrome associated with recurrent sinopulmonary and viral infections. We have recently identified a DOCK8-deficient mouse strain, carrying an ethylnitrosourea-induced splice-site mutation that shows a failure to mature a humoral immune response due to the loss of germinal centre B cells. In this study, we turned to T-cell immunity to investigate further the human immunodeficiency syndrome and its association with decreased peripheral CD4(+) and CD8(+) T cells. Characterisation of the DOCK8-deficient mouse revealed T-cell lymphopenia, with increased T-cell turnover and decreased survival. Egress of mature CD4(+) thymocytes was reduced with increased migration of these cells to the chemokine CXCL12. However, despite the two-fold reduction in peripheral naïve T cells, the DOCK8-deficient mice generated a normal primary CD8(+) immune response and were able to survive acute influenza virus infection. The limiting effect of DOCK8 was in the normal survival of CD8(+) memory T cells after infection. These findings help to explain why DOCK8-deficient patients are susceptible to recurrent infections and provide new insights into how T-cell memory is sustained.
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http://dx.doi.org/10.1002/eji.201141759DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3517112PMC
December 2011

Lymphatic endothelial cell sphingosine kinase activity is required for lymphocyte egress and lymphatic patterning.

J Exp Med 2010 Jan 21;207(1):17-27. Epub 2009 Dec 21.

Howard Hughes Medical Institute and Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, CA 94143, USA.

Lymphocyte egress from lymph nodes (LNs) is dependent on sphingosine-1-phosphate (S1P), but the cellular source of this S1P is not defined. We generated mice that expressed Cre from the lymphatic vessel endothelial hyaluronan receptor 1 (Lyve-1) locus and that showed efficient recombination of loxP-flanked genes in lymphatic endothelium. We report that mice with Lyve-1 CRE-mediated ablation of sphingosine kinase (Sphk) 1 and lacking Sphk2 have a loss of S1P in lymph while maintaining normal plasma S1P. In Lyve-1 Cre+ Sphk-deficient mice, lymphocyte egress from LNs and Peyer's patches is blocked. Treatment with pertussis toxin to overcome Galphai-mediated retention signals restores lymphocyte egress. Furthermore, in the absence of lymphatic Sphks, the initial lymphatic vessels in nonlymphoid tissues show an irregular morphology and a less organized vascular endothelial cadherin distribution at cell-cell junctions. Our data provide evidence that lymphatic endothelial cells are an in vivo source of S1P required for lymphocyte egress from LNs and Peyer's patches, and suggest a role for S1P in lymphatic vessel maturation.
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http://dx.doi.org/10.1084/jem.20091619DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2812554PMC
January 2010

Cortical sinus probing, S1P1-dependent entry and flow-based capture of egressing T cells.

Nat Immunol 2009 Jan 7;10(1):58-65. Epub 2008 Dec 7.

Howard Hughes Medical Institute and Department of Microbiology and Immunology, University of California San Francisco, San Francisco, California 94143, USA.

The cellular dynamics of the egress of lymphocytes from lymph nodes are poorly defined. Here we visualized the branched organization of lymph node cortical sinuses and found that after entry, some T cells were retained, whereas others returned to the parenchyma. T cells deficient in sphingosine 1-phosphate receptor type 1 probed the sinus surface but failed to enter the sinuses. In some sinuses, T cells became rounded and moved unidirectionally. T cells traveled from cortical sinuses into macrophage-rich sinus areas. Many T cells flowed from medullary sinuses into the subcapsular space. We propose a multistep model of lymph node egress in which cortical sinus probing is followed by entry dependent on sphingosine 1-phosphate receptor type 1, capture of cells in a sinus region with flow, and transport to medullary sinuses and the efferent lymph.
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http://dx.doi.org/10.1038/ni.1682DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2710451PMC
January 2009

S1P1 receptor signaling overrides retention mediated by G alpha i-coupled receptors to promote T cell egress.

Immunity 2008 Jan 27;28(1):122-33. Epub 2007 Dec 27.

Howard Hughes Medical Institute, University of California, San Francisco, CA 94143, USA.

The mechanism by which sphingosine-1-phosphate receptor-1 (S1P1) acts to promote lymphocyte egress from lymphoid organs is not defined. Here, we showed that CCR7-deficient T cells left lymph nodes more rapidly than wild-type cells did, whereas CCR7-overexpressing cells were retained for longer. After treatment with FTY720, an agonist that causes downmodulation of lymphocyte S1P1, CCR7-deficient T cells were less effectively retained than wild-type T cells. Moreover, treatment with pertussis toxin to inactivate signaling via G alpha i-protein-coupled receptors restored egress competence to S1P1-deficient lymphocytes. We also found that T cell accumulation in lymph node cortical sinusoids required intrinsic S1P1 expression and was antagonized by CCR7. These findings suggest a model where S1P1 acts in the lymphocyte to promote lymph node egress by overcoming retention signals mediated by CCR7 and additional G alpha i-coupled receptors. Furthermore, by simultaneously upregulating S1P1 and downregulating CCR7, T cells that have divided multiple times switch to a state favoring egress over retention.
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http://dx.doi.org/10.1016/j.immuni.2007.11.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2691390PMC
January 2008