Clinical Focus


  • Pediatric Infectious Diseases
  • Pediatrics

Professional Education


  • Board Certification: Pediatric Infectious Diseases, American Board of Pediatrics (2017)
  • Board Certification, American Board of Pediatrics, Pediatric Infectious Diseases
  • Board Certification, American Board of Pediatrics, General Pediatrics
  • Fellowship, Stanford University School of Medicine, Pediatric Infectious Diseases
  • Residency, Stanford University School of Medicine, Pediatrics
  • M.D., University of California, San Francisco, Medicine
  • Ph.D., University of California, San Francisco, Cell Biology/Immunology

All Publications


  • Pseudogenization of the Secreted Effector Gene sseI Confers Rapid Systemic Dissemination of S. Typhimurium ST313 within Migratory Dendritic Cells. Cell host & microbe Carden, S. E., Walker, G. T., Honeycutt, J., Lugo, K., Pham, T., Jacobson, A., Bouley, D., Idoyaga, J., Tsolis, R. M., Monack, D. 2017; 21 (2): 182-194

    Abstract

    Genome degradation correlates with host adaptation and systemic disease in Salmonella. Most lineages of the S. enterica subspecies Typhimurium cause gastroenteritis in humans; however, the recently emerged ST313 lineage II pathovar commonly causes systemic bacteremia in sub-Saharan Africa. ST313 lineage II displays genome degradation compared to gastroenteritis-associated lineages; yet, the mechanisms and causal genetic differences mediating these infection phenotypes are largely unknown. We find that the ST313 isolate D23580 hyperdisseminates from the gut to systemic sites, such as the mesenteric lymph nodes (MLNs), via CD11b(+) migratory dendritic cells (DCs). This hyperdissemination was facilitated by the loss of sseI, which encodes an effector that inhibits DC migration in gastroenteritis-associated isolates. Expressing functional SseI in D23580 reduced the number of infected migratory DCs and bacteria in the MLN. Our study reveals a mechanism linking pseudogenization of effectors with the evolution of niche adaptation in a bacterial pathogen.

    View details for DOI 10.1016/j.chom.2017.01.009

    View details for PubMedID 28182950

    View details for PubMedCentralID PMC5325708

  • DOCK8 is essential for T-cell survival and the maintenance of CD8(+) T-cell memory EUROPEAN JOURNAL OF IMMUNOLOGY Lambe, T., Crawford, G., Johnson, A. L., Crockford, T. L., Bouriez-Jones, T., Smyth, A. M., Pham, T. H., Zhang, Q., Freeman, A. F., Cyster, J. G., Su, H. C., Cornall, R. J. 2011; 41 (12): 3423-3435

    Abstract

    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.

    View details for DOI 10.1002/eji.201141759

    View details for Web of Science ID 000297465000009

    View details for PubMedID 21969276

  • GRK2-Dependent S1PR1 Desensitization Is Required for Lymphocytes to Overcome Their Attraction to Blood SCIENCE Arnon, T. I., Xu, Y., Lo, C., Trung Pham, T., An, J., Coughlin, S., Dorn, G. W., Cyster, J. G. 2011; 333 (6051): 1898-1903

    Abstract

    Lymphocytes egress from lymphoid organs in response to sphingosine-1-phosphate (S1P); minutes later they migrate from blood into tissue against the S1P gradient. The mechanisms facilitating cell movement against the gradient have not been defined. Here, we show that heterotrimeric guanine nucleotide-binding protein-coupled receptor kinase-2 (GRK2) functions in down-regulation of S1P receptor-1 (S1PR1) on blood-exposed lymphocytes. T and B cell movement from blood into lymph nodes is reduced in the absence of GRK2 but is restored in S1P-deficient mice. In the spleen, B cell movement between the blood-rich marginal zone and follicles is disrupted by GRK2 deficiency and by mutation of an S1PR1 desensitization motif. Moreover, delivery of systemic antigen into follicles is impaired. Thus, GRK2-dependent S1PR1 desensitization allows lymphocytes to escape circulatory fluids and migrate into lymphoid tissues.

    View details for DOI 10.1126/science.1208248

    View details for Web of Science ID 000295365800059

    View details for PubMedID 21960637

    View details for PubMedCentralID PMC3267326

  • Lymphatic endothelial cell sphingosine kinase activity is required for lymphocyte egress and lymphatic patterning JOURNAL OF EXPERIMENTAL MEDICINE Pham, T. H., Baluk, P., Xu, Y., Grigorova, I., Bankovich, A. J., Pappu, R., Coughlin, S. R., McDonald, D. M., Schwab, S. R., Cyster, J. G. 2010; 207 (1): 17-27

    Abstract

    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.

    View details for DOI 10.1084/jem.20091619

    View details for Web of Science ID 000273690800003

    View details for PubMedID 20026661

    View details for PubMedCentralID PMC2812554

  • Sphingosine-1-phosphate in the plasma compartment regulates basal and inflammation-induced vascular leak in mice JOURNAL OF CLINICAL INVESTIGATION Camerer, E., Regard, J. B., Cornelissen, I., Srinivasan, Y., Duong, D. N., Palmer, D., Pham, T. H., Wong, J. S., Pappu, R., Coughlin, S. R. 2009; 119 (7): 1871-1879

    Abstract

    Maintenance of vascular integrity is critical for homeostasis, and temporally and spatially regulated vascular leak is a central feature of inflammation. Sphingosine-1-phosphate (S1P) can regulate endothelial barrier function, but the sources of the S1P that provide this activity in vivo and its importance in modulating different inflammatory responses are unknown. We report here that mutant mice engineered to selectively lack S1P in plasma displayed increased vascular leak and impaired survival after anaphylaxis, administration of platelet-activating factor (PAF) or histamine, and exposure to related inflammatory challenges. Increased leak was associated with increased interendothelial cell gaps in venules and was reversed by transfusion with wild-type erythrocytes (which restored plasma S1P levels) and by acute treatment with an agonist for the S1P receptor 1 (S1pr1). S1pr1 agonist did not protect wild-type mice from PAF-induced leak, consistent with plasma S1P levels being sufficient for S1pr1 activation in wild-type mice. However, an agonist for another endothelial cell Gi-coupled receptor, Par2, did protect wild-type mice from PAF-induced vascular leak, and systemic treatment with pertussis toxin prevented rescue by Par2 agonist and sensitized wild-type mice to leak-inducing stimuli in a manner that resembled the loss of plasma S1P. Our results suggest that the blood communicates with blood vessels via plasma S1P to maintain vascular integrity and regulate vascular leak. This pathway prevents lethal responses to leak-inducing mediators in mouse models.

    View details for DOI 10.1172/JCI38575

    View details for Web of Science ID 000267694300016

    View details for PubMedID 19603543

  • Cortical sinus probing, S1P(1)-dependent entry and flow-based capture of egressing T cells NATURE IMMUNOLOGY Grigorova, I. L., Schwab, S. R., Phan, T. G., Pham, T. H., Okada, T., Cyster, J. G. 2009; 10 (1): 58-65

    Abstract

    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.

    View details for DOI 10.1038/ni.1682

    View details for Web of Science ID 000261788800012

    View details for PubMedID 19060900

  • S1P(1) receptor signaling overrides retention mediated by G alpha(i)-coupled receptors to promote T cell egress IMMUNITY Pham, T. H., Okada, T., Matioubian, M., Lo, C. G., Cyster, J. G. 2008; 28 (1): 122-133

    Abstract

    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.

    View details for DOI 10.1016/j.immuni.2007.11.017

    View details for Web of Science ID 000252627300016

    View details for PubMedID 18164221

    View details for PubMedCentralID PMC2691390

  • Epistasis between mouse Klra and major histocompatibility complex class I loci is associated with a new mechanism of natural killer cell-mediated innate resistance to cytomegalovirus infection NATURE GENETICS Desrosiers, M. P., Kielczewska, A., Loredo-Osti, J. C., Adam, S. G., Makrigiannis, A. P., Lemieux, S., Pham, T., Lodoen, M. B., Morgan, K., Lanier, L. L., Vidal, S. M. 2005; 37 (6): 593-599

    Abstract

    Experimental infection with mouse cytomegalovirus (MCMV) has been used to elucidate the intricate host-pathogen mechanisms that determine innate resistance to infection. Linkage analyses in F(2) progeny from MCMV-resistant MA/My (H2 (k)) and MCMV-susceptible BALB/c (H2 (d)) and BALB.K (H2 (k)) mouse strains indicated that only the combination of alleles encoded by a gene in the Klra (also called Ly49) cluster on chromosome 6, and one in the major histocompatibility complex (H2) on chromosome 17, is associated with virus resistance. We found that natural killer cell-activating receptor Ly49P specifically recognized MCMV-infected cells, dependent on the presence of the H2 (k) haplotype. This binding was blocked using antibodies to H-2D(k) but not antibodies to H-2K(k). These results are suggestive of a new natural killer cell mechanism implicated in MCMV resistance, which depends on the functional interaction of the Ly49P receptor and the major histocompatibility complex class I molecule H-2D(k) on MCMV-infected cells.

    View details for DOI 10.1038/ng1564

    View details for Web of Science ID 000229495300012

    View details for PubMedID 15895081