Date of Award

5-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Field of Study

Microbiology and Immunology

Department

Graduate School of Biomedical Sciences

First Advisor

Jerry Simecka

Abstract

The purpose of these studies was to examine the role of regulatory T cells (Tregs) in mycoplasma respiratory disease. Depletion of Tregs resulted in increased disease severity. Tregdepleted mice lost significantly more weight over the course of the experiment, and displayed a significantly higher incidence of both gross lung lesions and histological lung lesions at day 14 post-infection. Treg depletion resulted in increased cell infiltration into the lungs by day 14 postinfection, and significant increases in the serum levels of mycoplasma-specific antibodies. Treg depletion also led to an increase in the percentage of IL-13+ T cells in the LRNs, meaning that the immune response was skewed towards a Th2 phenotype. There were no differences observed in lung CFU. These data demonstrate that Tregs in mycoplasma respiratory disease play a role in inflammation and disease severity, but have no effect on bacterial clearance. Importantly, depletion of Tregs causes a Th2-directed shift in the immune response.

Additional studies demonstrated that Tregs from mycoplasma-infected mice secreted IFN-γ or IL-17. IFN-γ + and IL-17+ Treg populations both preferentially expanded in response to M. pulmonis infection. Depletion of Tregs resulted in decreased secretion of IFN-γ and IL-17 by CD4+ non-Treg cells. Cocultures of Tregs and T helper cells from mycoplasmainfected mice secreted large amounts of IFN-γ and IL-17 when stimulated with mycoplasma membrane antigen. Levels of IL-4, IL-10, and IL-13 did not significantly increase in response to antigen. Together these studies demonstrate that mycoplasma respiratory disease is influenced by Tregs. These data further suggest that mycoplasma-specific Tregs include two unique subpopulations that express either IFN-γ or IL-17, and that these Tregs may promote the secretion of IFN-γ and IL-17 by T helper cells. This may represent a novel mechanism of Tregmediated immune suppression. This knowledge can assist in the development of treatments for mycoplasma respiratory disease and in the development of Treg-mediated therapies for a number of diseases.

Comments

Odeh, Adam N., The Role of Regulatory T Cells in Mycoplasma Respiratory Infection. Doctor of Philosophy (Molecular Biology and Immunology), May 2011, 104 pp., 2 tables, 23 illustrations, bibliography, 137 titles.

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