Semester

Spring

Date of Graduation

2013

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Microbiology, Immunology, and Cell Biology

Committee Chair

Donald H Beezhold

Committee Co-Chair

Kathleen M Brundage

Committee Member

Slawomir Lukomski

Committee Member

Rosana Schafer

Committee Member

Paul D. Siegel.

Abstract

Personal exposures to A. fumigatus are associated with a variety of adverse health outcomes, including invasive aspergillosis, allergic sensitization, and asthma. Due to the high rate of mortality associated with invasive disease in immunocompromised patients, most studies of A. fumigatus have aimed to characterize the immune responses in immunocompromised murine models. However, a larger portion of the population is affected by fungal-induced allergies and asthma and the immune mechanisms associated with exposure have rarely been studied in an immunocompetent model. These models do not accurately reflect the natural method of exposure to environmental sources of conidia, and may significantly impact responses between fungi and the host immune system. Furthermore, little is known about the mechanisms associated with fungal induced allergy and asthma. Persistence of antigen is believed to play a role in induction of these diseases. Melanin, an A. fumigatus virulence factor, protects conidia from innate clearance, leading to fungal persistence. However, it remains unknown if melanin influences the induction of A. fumigatus -- specific allergy and/or asthma. In these studies, immunocompetent mice were repeatedly exposed to A. fumigatus wild-type (WT) or melanin deficient conidia via aspiration or dry conidial exposures via an acoustical generator. Histopathological analysis of lung sections showed moderate to severe inflammation in all exposed mice, regardless of the exposure method or melanin content of the conidia. Overall, flow cytometric analysis of bronchoalveolar lavage fluid was similar between the exposure methods. However, there were marked differences between WT and melanin-deficient exposure groups in many of the cell populations analyzed. Germination was evident in all mice exposed to WT conidia, despite the exposure method. However, melanin-deficient conidia did not germinate, and were also cleared more rapidly in both exposure groups. Enhanced clearance of the melanin-deficient conidia was evident in mice exposed via the acoustical generator when compared to the aspiration exposure groups. Importantly, CD8+IL-17+ Tc17 cells were elevated above control groups in all exposed mice, regardless of the exposure method, though the numbers were significantly increased in mice exposed to WT conidia. This is a significant finding, as the presence of these cells has not been previously reported in the context of A. fumigatus-induced immune responses. Evidence also suggests that the induction of Tc17 cells may be influenced by WT germination. Taken together, the data presented in this dissertation are among the first to characterize the immune responses to repeated dry fungal exposures in immunocompetent animals. Because these studies proved the feasibility of the dry aerosol model for repeated exposures, future studies with different environmentally prevalent fungi can be adapted for use with the acoustical generator to provide more accurate analysis of immune responses following repeated dry exposures.

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