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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2013)

Infectious diseases affect individuals all over the world. Both vector-borne and non-vector pathogens that cause these illnesses have developed strategies to subvert immune recognition. Since the innate immune system is the first line of defense against potentially noxious substances, the host is also able to adjust innate immune signaling in order to perpetuate its survival. This host-pathogen interaction is highly conserved, ranging from plants to mammals. Unfortunately, there remains quite a disparity between the plethora of pathogens and what is known about host signaling in response to their recognition. Deciphering the modes by which vector-borne and non-vector-borne pathogens influence host signaling will ultimately provide a clearer understanding of targets for protective measures against these life-threatening diseases.

The nod-like receptors (NLRs) are crucial components for host protection from a wide array of pathogen and danger associated molecular patterns. Whether they act alone or as a protein platform, NLRs effectively initiate key innate immune signaling cascades in order to promote the expression and/or secretion of pro-inflammatory genes and cytokines. Additionally, the inflammasome, a protein scaffold formed by NLRs/AIM2, the ASC adaptor molecule, and caspase-1 can elicit a potent form of cell death triggered by inflammation called pyroptosis. As a result, NLRs are very attractive to both the host and the pathogen: (1) for the host, it provides a method by which it can protect itself from intracellular detection of pathogens, while (2) for the pathogen, it is a target for manipulation so that it may propagate. This dissertation will provide an overview and insight regarding vector-borne and non-vector-borne pathogens and their effects on NLR signaling pathways.

    Cover page: Manipulation of Host Signaling by Vector-Borne and Non-Vector-Borne Pathogens
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2015)
    M cells are a subset of mucosal epithelial cells with specialized capability to transport antigens across the mucosal barrier, but there is limited information on antigen transfer in the subepithelial zone due to the challenges in tracking microparticles and antigens that are transcytosed by this unique cell. Using transgenic reporter mice expressing dsRed in the cytoplasm of M cells and EGFP in myeloid cells, we observed that the M cell basolateral pocket hosts a close interaction between B lymphocytes and dendritic cells. Interestingly, we identified a population of previously undescribed M cell-derived vesicles (MCM) that are constitutively shed into the subepithelial space and readily taken up by CX3CR1(+)CD11b(+) CD11c(+) dendritic cells. These MCM are characterized by their cytoplasmic dsRed confirming their origin from the M cell cytoplasm. MCM showed preferential colocalization in dendritic cells with transcytosed bacteria but not transcytosed polystyrene beads, indicating a selective sorting of cargo fate in the subepithelial zone. The size and number of MCM were found to be upregulated by bacterial transcytosis and soluble toll-like receptor 2 (TLR2) agonist, further pointing to dynamic regulation of this mechanism. These results suggest that MCM provide a unique function by delivering to dendritic cells, various materials such as M cell-derived proteins, effector proteins, toxins, and particles found in the M cell cytoplasm during infection or surveillance.
      Cover page: M cell-derived vesicles suggest a unique pathway for trans-epithelial antigen delivery
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2012)
      Abstract Background Ixodes scapularis saliva enables the transmission of infectious agents to the mammalian host due to its immunomodulatory, anesthetic and anti-coagulant properties. However, how I. scapularis saliva influences host cytokine secretion in the presence of the obligate intracellular rickettsial pathogen Anaplasma phagocytophilum remains elusive. Methods Bone marrow derived macrophages (BMDMs) were stimulated with pathogen associated molecular patterns (PAMPs) and A. phagocytophilum. Cytokine secretion was measured in the presence and absence of I. scapularis saliva. Human peripheral blood mononuclear cells (PBMCs) were also stimulated with Tumor Necrosis Factor (TNF)-α in the presence and absence of I. scapularis saliva and interleukin (IL)-8 was measured. Results I. scapularis saliva inhibits inflammatory cytokine secretion by macrophages during stimulation of Toll-like (TLR) and Nod-like receptor (NLR) signaling pathways. The effect of I. scapularis saliva on immune cells is not restricted to murine macrophages because decreasing levels of interleukin (IL)-8 were observed after TNF-α stimulation of human peripheral blood mononuclear cells. I. scapularis saliva also mitigates pro-inflammatory cytokine response by murine macrophages during challenge with A. phagocytophilum. Conclusions These findings suggest that I. scapularis may inhibit inflammatory cytokine secretion during rickettsial transmission at the vector-host interface.
        Cover page: Ixodes scapularis saliva mitigates inflammatory cytokine secretion during Anaplasma phagocytophilum stimulation of immune cells
        • Article
        • Peer Reviewed
        UC Riverside Previously Published Works (2012)
        Background

        Ixodes scapularis saliva enables the transmission of infectious agents to the mammalian host due to its immunomodulatory, anesthetic and anti-coagulant properties. However, how I. scapularis saliva influences host cytokine secretion in the presence of the obligate intracellular rickettsial pathogen Anaplasma phagocytophilum remains elusive.

        Methods

        Bone marrow derived macrophages (BMDMs) were stimulated with pathogen associated molecular patterns (PAMPs) and A. phagocytophilum. Cytokine secretion was measured in the presence and absence of I. scapularis saliva. Human peripheral blood mononuclear cells (PBMCs) were also stimulated with Tumor Necrosis Factor (TNF)-α in the presence and absence of I. scapularis saliva and interleukin (IL)-8 was measured.

        Results

        I. scapularis saliva inhibits inflammatory cytokine secretion by macrophages during stimulation of Toll-like (TLR) and Nod-like receptor (NLR) signaling pathways. The effect of I. scapularis saliva on immune cells is not restricted to murine macrophages because decreasing levels of interleukin (IL)-8 were observed after TNF-α stimulation of human peripheral blood mononuclear cells. I. scapularis saliva also mitigates pro-inflammatory cytokine response by murine macrophages during challenge with A. phagocytophilum.

        Conclusions

        These findings suggest that I. scapularis may inhibit inflammatory cytokine secretion during rickettsial transmission at the vector-host interface.

          • Article
          • Peer Reviewed
          UC Riverside Previously Published Works (2013)
          Ubiquitination is a posttranslational modification that regulates protein degradation and signaling in eukaryotes. Although it is acknowledged that pathogens exploit ubiquitination to infect mammalian cells, it remains unknown how microbes interact with the ubiquitination machinery in medically relevant arthropods. Here, we show that the ubiquitination machinery is present in the tick Ixodes scapularis and demonstrate that the E3 ubiquitin ligase named x-linked inhibitor of apoptosis protein (XIAP) restricts bacterial colonization of this arthropod vector. We provide evidence that xiap silencing significantly increases tick colonization by the bacterium Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis. We also demonstrate that (i) XIAP polyubiquitination is dependent on the really interesting new gene (RING) catalytic domain, (ii) XIAP polyubiquitination occurs via lysine (K)-63 but not K-48 residues, and (iii) XIAP-dependent K-63 polyubiquitination requires zinc for catalysis. Taken together, our data define a role for ubiquitination during bacterial colonization of disease vectors.
            • Article
            • Peer Reviewed
            UC Riverside Previously Published Works (2013)
            Ubiquitination is a posttranslational modification that regulates protein degradation and signaling in eukaryotes. Although it is acknowledged that pathogens exploit ubiquitination to infect mammalian cells, it remains unknown how microbes interact with the ubiquitination machinery in medically relevant arthropods. Here, we show that the ubiquitination machinery is present in the tick Ixodes scapularis and demonstrate that the E3 ubiquitin ligase named x-linked inhibitor of apoptosis protein (XIAP) restricts bacterial colonization of this arthropod vector. We provide evidence that xiap silencing significantly increases tick colonization by the bacterium Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis. We also demonstrate that (i) XIAP polyubiquitination is dependent on the really interesting new gene (RING) catalytic domain, (ii) XIAP polyubiquitination occurs via lysine (K)-63 but not K-48 residues, and (iii) XIAP-dependent K-63 polyubiquitination requires zinc for catalysis. Taken together, our data define a role for ubiquitination during bacterial colonization of disease vectors.
              Cover page: The E3 Ubiquitin Ligase XIAP Restricts Anaplasma phagocytophilum Colonization of Ixodes scapularis Ticks
              • Article
              • Peer Reviewed
              UC Riverside Previously Published Works (2012)

              Anaplasma phagocytophilum is a tick-borne rickettsial pathogen that provokes an acute inflammatory response during mammalian infection. The illness caused by A. phagocytophilum, human granulocytic anaplasmosis, occurs irrespective of pathogen load and results instead from host-derived immunopathology. Thus, characterizing A. phagocytophilum genes that affect the inflammatory process is critical for understanding disease etiology. By using an A. phagocytophilum Himar1 transposon mutant library, we showed that a single transposon insertion into the A. phagocytophilum dihydrolipoamide dehydrogenase 1 gene (lpda1 [APH_0065]) affects inflammation during infection. A. phagocytophilum lacking lpda1 revealed enlargement of the spleen, increased splenic extramedullary hematopoiesis, and altered clinicopathological abnormalities during mammalian colonization. Furthermore, LPDA1-derived immunopathology was independent of neutrophil infection and correlated with enhanced reactive oxygen species from NADPH oxidase and nuclear factor (NF)-κB signaling in macrophages. Taken together, these findings suggest the presence of different signaling pathways in neutrophils and macrophages during A. phagocytophilum invasion and highlight the importance of LPDA1 as an immunopathological molecule.

                • Article
                • Peer Reviewed
                UC Riverside Previously Published Works (2014)
                Saliva from arthropod vectors facilitates blood feeding by altering host inflammation. Whether arthropod saliva counters inflammasome signaling, a protein scaffold that regulates the activity of caspase-1 and cleavage of interleukin-1β (IL-1β) and IL-18 into mature molecules, remains elusive. In this study, we provide evidence that a tick salivary protein, sialostatin L2, inhibits inflammasome formation during pathogen infection. We show that sialostatin L2 targets caspase-1 activity during host stimulation with the rickettsial agent Anaplasma phagocytophilum. A. phagocytophilum causes macrophage activation and hemophagocytic syndrome features. The effect of sialostatin L2 in macrophages was not due to direct caspase-1 enzymatic inhibition, and it did not rely on nuclear factor κB or cathepsin L signaling. Reactive oxygen species from NADPH oxidase and the Loop2 domain of sialostatin L2 were important for the regulatory process. Altogether, our data expand the knowledge of immunoregulatory pathways of tick salivary proteins and unveil an important finding in inflammasome biology.
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