Year of Publication

2009

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Graduate School

Department

Toxicology

First Advisor

Dr. J.Scott Bryson

Abstract

Syngeneic graft-versus-host disease (SGVHD) is induced by reconstituting lethally irradiated mice with syngeneic BM cells followed by a 21 day treatment with the immunosuppressive agent cyclosporine A (CsA). Clinical symptoms of the disease appear 2-3 weeks following cessation of CsA therapy and disease-associated inflammation occurs primarily in the colon and liver.

The development of SGVHD is a complex process resulting from the cooperative interaction of multiple effector cell populations including NK cells, T cells and macrophages. TH1 cytokines (IL-12, TNF-α, IFN- γ), produced by these effector cells, serve as inflammatory mediators contributing to the pathogenesis of SGVHD. The SGVHD conditioning agents, irradiation and CsA, are both required for the development of disease and contribute to the production of oxidative stress. Time course studies revealed increased reactive oxygen and nitrogen species (ROS/RNS), as well as, increased colon mRNA levels for TNF-α and iNOS in CsA-treated versus control BMT animals. Since ROS/RNS are known to mediate CsA toxicity, studies were undertaken to determine the effect of oxidative stress on the induction of SGVHD. In vivo treatment with the antioxidant MnTBAP caused a reduction in colon mRNA levels for iNOS and TNF-α, as well as delayed disease development, suggesting a role for oxidative stress in the development of SGVHD.

In addition, CD4+ T cells have been shown to play an important role in the inflammatory response observed in the gut of SGVHD mice. Time course studies revealed significant increases in the migration of CD4+ T cells as early as day 14 post- BMT into the colon of CsA mice as well as significant elevated mRNA levels of cell adhesion molecules. Homing studies revealed that a labeled CD4+ T cell line, generated from SGVHD mice, migrated in larger numbers into the gut of CsA-treated mice compared to control animals. This study demonstrated that CD4+ T cells responsible for the pathogenesis observed in murine SGVHD are present early after BMT in colons of CsA-treated mice, suggesting that during the 21 days of immunosuppression therapy functional mechanisms are in place that result in increased homing of effector cells to colons of CsA-treated mice.

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