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Rickettsial Infection of Humanized Mice
Institution: University of Texas Medical Branch (UTMB), Galveston, TX
Principal Investigator: Gustavo Valbuena, MD, PhD
Co-Investigator: D. Mark Estes, PhD – UTMB, Galveston, TX
Expected Product: Animal model for epidemic typhus and Rocky Mountain spotted fever.
Description: Our long-term goal is to elucidate the complex immunological and pathological mechanisms of humans in response to agents whose pathogenesis involves the cells lining the vasculature (endothelial cells), particularly rickettsiae. These arthropod-borne obligately intracellular bacteria include the agents of Rocky Mountain spotted fever (Rickettsia rickettsii) and epidemic typhus (R. prowazekii). They are among the most lethal pathogens known to man (case fatality rate of 20-30% in untreated cases), and they are designated select agents with potential use for bioterrorism. Relevant data from humans have lagged behind those derived from the animal models due mainly to the difficulty in correctly identifying cases of rickettsioses. This gap in knowledge has prevented the discovery of novel targets of intervention. Our objective is to develop humanized mouse models of epidemic typhus and Rocky Mountain spotted fever as paradigms for other infectious diseases in which endothelial cells are involved in the pathogenesis. The hypothesis is that humanized mice develop rickettsia-triggered vascular lesions and adaptive immune responses against rickettsiae. The specific aims are to identify the types of human leukocytes that infiltrate rickettsia-infected human vascular beds in humanized mice and to measure the human B- and T-cell-mediated anti-rickettsial immune responses in humanized mice. The experimental approaches include the identification of infiltrating leukocytes in humanized mice infected with R. prowazekii or R. rickettsii and measurement of rickettsial loads in synthetic human vascular beds, and determination of human immunoglobulin subtypes of anti-rickettsiae antibodies and antigen-specific human T-cell proliferation, cytokine production, and cytotoxicity in humanized mice infected with rickettsiae. The humanized mice will allow: (1) the identification of targets of therapeutic intervention and of protective antigens recognized by humans for vaccine development; (2) the study of the in vivo interactions between human leukocytes and rickettsia-infected endothelial cells; (3) the determination of the mechanism(s) of vascular leakage, a central feature of the pathogenesis of these diseases; (4) the evaluation of natural and vaccine-induced immune responses; and (5) the testing of immunogenicity and protection of candidate vaccines. In addition, it will provide a new model system to study the immunobiology of the human endothelium during infections that involve endothelial cells in their pathogenesis; most of these infections are caused by agents on NIAID’s list of biothreat select agents. The work proposed here is feasible because of our experience with similar models and because we have appropriate human and material resources for Biosafety Level 3 work. |
