Browsing by Author "Carrasco, Sebastian E."

Now showing 1 - 4 of 4
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    Borrelia burgdorferi elongation factor EF-Tu is an immunogenic protein during Lyme borreliosis
    (Nature, 2015-09) Carrasco, Sebastian E.; Yang, Youyun; Troxell, Bryan; Yang, Xiuli; Pal, Utpal; Yang, X. Frank; Department of Microbiology & Immunology, IU School of Medicine
    Borrelia burgdorferi, the etiological agent of Lyme disease, does not produce lipopolysaccharide but expresses a large number of lipoproteins on its cell surface. These outer membrane lipoproteins are highly immunogenic and have been used for serodiagnosis of Lyme disease. Recent studies have shown that highly conserved cytosolic proteins such as enolase and elongation factor Tu (EF-Tu) unexpectedly localized on the surface of bacteria including B. burgdorferi, and surface-localized enolase has shown to contribute to the enzootic cycle of B. burgdorferi. In this study, we studied the immunogenicity, surface localization, and function of B. burgdorferi EF-Tu. We found that EF-Tu is highly immunogenic in mice, and EF-Tu antibodies were readily detected in Lyme disease patients. On the other hand, active immunization studies showed that EF-Tu antibodies did not protect mice from infection when challenged with B. burgdorferi via either needle inoculation or tick bites. Borrelial mouse-tick cycle studies showed that EF-Tu antibodies also did not block B. burgdorferi migration and survival in ticks. Consistent with these findings, we found that EF-Tu primarily localizes in the protoplasmic cylinder of spirochetes and is not on the surface of B. burgdorferi. Taken together, our studies suggest that B. burgdorferi EF-Tu is not surfaced exposed, but it is highly immunogenic and is a potential serodiagnostic marker for Lyme borreliosis.
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    Outer surface protein OspC is an antiphagocytic factor that protects Borrelia burgdorferi from phagocytosis by macrophages
    (American Society for Microbiology, 2015-12) Carrasco, Sebastian E.; Troxell, Bryan; Yang, Youyun; Brandt, Stephanie L.; Li, Hongxia; Sandusky, George E.; Condon, Keith W.; Serezani, C. Henrique; Yang, X. Frank; Department of Microbiology & Immunology, IU School of Medicine
    Outer surface protein C (OspC) is one of the major lipoproteins expressed on the surface of Borrelia burgdorferi during tick feeding and the early phase of mammalian infection. OspC is required for B. burgdorferi to establish infection in both immunocompetent and SCID mice and has been proposed to facilitate evasion of innate immune defenses. However, the exact biological function of OspC remains elusive. In this study, we showed that the ospC-deficient spirochete could not establish infection in NOD-scid IL2rγ(null) mice that lack B cells, T cells, NK cells, and lytic complement. The ospC mutant also could not establish infection in anti-Ly6G-treated SCID and C3H/HeN mice (depletion of neutrophils). However, depletion of mononuclear phagocytes at the skin site of inoculation in SCID and C3H/HeN mice allowed the ospC mutant to establish infection in vivo. In phagocyte-depleted mice, the ospC mutant was able to colonize the joints and triggered neutrophilia during dissemination. Furthermore, we found that phagocytosis of green fluorescent protein (GFP)-expressing ospC mutant spirochetes by murine peritoneal macrophages and human THP-1 macrophage-like cells, but not in PMN-HL60, was significantly higher than parental wild-type B. burgdorferi strains, suggesting that OspC has an antiphagocytic property. In addition, overproduction of OspC in spirochetes also decreased the uptake of spirochetes by murine peritoneal macrophages. Together, our findings provide evidence that mononuclear phagocytes play a key role in clearance of the ospC mutant and that OspC promotes spirochetes' evasion of macrophages during early Lyme borreliosis.
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    Positive and Negative Regulation of Glycerol Utilization by the c-di-GMP Binding Protein PlzA in Borrelia burgdorferi
    (American Society for Microbiology, 2018-10-23) Zhang, Jun-Jie; Chen, Tong; Yang, Youyun; Du, Jimei; Li, Hongxia; Troxell, Bryan; He, Ming; Carrasco, Sebastian E.; Gomelsky, Mark; Yang, X. Frank; Microbiology and Immunology, School of Medicine
    Borrelia burgdorferi, the causative agent of Lyme disease, encounters two disparate host environments during its enzootic life cycle, Ixodes ticks and mammalian hosts. B. burgdorferi has a small genome that encodes a streamlined cyclic dimeric GMP (c-di-GMP) signaling system comprising a single diguanylate cyclase, Rrp1, and two phosphodiesterases. This system is essential for spirochete survival in ticks, in part because it controls the expression of the glp operon involved in glycerol utilization. In this study, we showed that a B. burgdorferi c-di-GMP receptor, PlzA, functions as both a positive and a negative regulator for glp expression. Deletion of plzA or mutation in plzA that impaired c-di-GMP binding abolished glp expression. On the other hand, overexpression of plzA resulted in glp repression, which could be rescued by simultaneous overexpression of rrp1. plzA overexpression in the rrp1 mutant, which is devoid of c-di-GMP, or overexpression of a plzA mutant incapable of c-di-GMP binding further enhanced glp repression. Combined results suggest that c-di-GMP-bound PlzA functions as a positive regulator, whereas ligand-free PlzA acts as a negative regulator for glp expression. Thus, PlzA of B. burgdorferi with a streamlined c-di-GMP signaling system not only controls multiple targets, as previously envisioned, but has also evolved different modes of action.IMPORTANCE The Lyme disease pathogen, Borrelia burgdorferi, has a simple cyclic dimeric GMP (c-di-GMP) signaling system essential for adaptation of the pathogen to the complicated tick environment. The c-di-GMP effector of B. burgdorferi, PlzA, has been shown to regulate multiple cellular processes, including motility, osmolality sensing, and nutrient utilization. The findings of this study demonstrate that PlzA not only controls multiple targets but also has different functional modalities, allowing it to act as both positive and negative regulator of the glp operon expression. This work highlights how bacteria with a small genome can compensate for the limited regulatory repertoire by increasing the complexity of targets and modes of action in their regulatory proteins.
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    Toll-like receptor 3 (TLR3) promotes the resolution of Chlamydia muridarum genital tract infection in congenic C57BL/6N mice
    (Public Library of Science, 2018-04-06) Carrasco, Sebastian E.; Hu, Sishun; Imai, Denise M.; Kumar, Ramesh; Sandusky, George E.; Yang, X. Frank; Derbigny, Wilbert A.; Microbiology and Immunology, School of Medicine
    Chlamydia trachomatis urogenital serovars primarily replicate in epithelial cells lining the reproductive tract. Epithelial cells recognize Chlamydia through cell surface and cytosolic receptors, and/or endosomal innate receptors such as Toll-like receptors (TLRs). Activation of these receptors triggers both innate and adaptive immune mechanisms that are required for chlamydial clearance, but are also responsible for the immunopathology in the reproductive tract. We previously demonstrated that Chlamydia muridarum (Cm) induces IFN-β in oviduct epithelial cells (OE) in a TLR3-dependent manner, and that the synthesis of several cytokines and chemokines are diminished in Cm-challenged OE derived from TLR3-/- 129S1 mice. Furthermore, our in vitro studies showed that Cm replication in TLR3-/- OE is more efficient than in wild-type OE. Because TLR3 modulates the release inflammatory mediators involved in host defense during Cm infection, we hypothesized that TLR3 plays a protective role against Cm-induced genital tract pathology in congenic C57BL/6N mice. Using the Cm mouse model for human Chlamydia genital tract infections, we demonstrated that TLR3-/- mice had increased Cm shedding during early and mid-stage genital infection. In early stage infection, TLR3-/- mice showed a diminished synthesis of IFN-β, IL-1β, and IL-6, but enhanced production of IL-10, TNF-α, and IFN-γ. In mid-stage infection, TLR3-/- mice exhibited significantly enhanced lymphocytic endometritis and salpingitis than wild-type mice. These lymphocytes were predominantly scattered along the endometrial stroma and the associated smooth muscle, and the lamina propria supporting the oviducts. Surprisingly, our data show that CD4+ T-cells are significantly enhanced in the genital tract TLR3-/- mice during mid-stage Chlamydial infection. In late-stage infections, both mouse strains developed hydrosalpinx; however, the extent of hydrosalpinx was more severe in TLR3-/- mice. Together, these data suggest that TLR3 promotes the clearance of Cm during early and mid-stages of genital tract infection, and that loss of TLR3 is detrimental in the development hydrosalpinx.