Date of Award

5-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Interdisciplinary Program

Research Advisor

Edward Rosloniec, Ph.D.

Committee

Elizabeth Fitzpatrick, Ph.D. Terrence Geiger, Ph.D. Tony Marion, Ph.D. Marko Radic, Ph.D

Abstract

The etiology of the autoimmune disease rheumatoid arthritis (RA) is unknown, but the role of cytokines, including IFN-g, as effectors of immune cell function has been established by the examination of cytokine production in RA patients and through the use of animal models. C57BL/6 (B6) mice that express MHC class II molecules of the b haplotype (I-Ab) are not typically susceptible to collagen-induced arthritis (CIA), the most widely studied animal model of RA. When the gene encoding IFN-g is removed by genetic deletion, however, susceptibility to CIA is conferred. In addition, T cell responses against the immunogen that stimulates CIA, type II collagen (CII), are reduced in the B6 strain when compared to susceptible mouse strains that express differing MHC haplotypes such as the I-Aq-expressing DBA mouse. These observations led to the development of the following hypothesis. IFN-g functions as a regulator of T cell responses to weak determinants, and I-Ab MHC class II molecules have low affinity for collagen autoantigen determinants. In the IFN-g-/- B6 mouse, the absence of IFN-g alters T cell function and cytokine production following immunization with CII, disrupting normal immune function and allowing the development of CIA.

To reveal the pathogenic mechanisms that mediate susceptibility to arthritis in the B6 IFN-g-/- mouse we examined several aspects of the immune response that follows immunization with CII. Firstly, alterations in cellular immune responses between wild type and B6 IFN-g-/-mice were examined following immunization with CII. Secondly, an antigenic determinant present in bovine CII that stimulates T cell response in mice expressing I-Ab was identified. This determinant was identified by the use of direct binding assays between I-Ab and CII derived peptides as well as by the generation of T hybridomas generated in I-Ab-expressing mice that respond to CII. In a second series of experiments, the role of IFN-g in modulating disease progression was examined by the use of microarray analysis to identify genes that are altered between wild type and IFN‑g‑/‑ B6 mice immunized with CII in CFA emulsion. This allowed the identification of IL-17 and IL-18 Binding Protein (IL-18 BP) as differentially expressed between the two strains. When IL-18 BP was given exogenously to IFN-g-/- B6 mice immunized with CII, the mice were protected from the development of CIA.

These results indicate that a CII determinant is present in bovine CII and the low immunogenic properties of this determinant may be responsible for the lack of arthritis development in wild type B6 mice. In the absence of IFN-g, there is disregulation of immune function exhibited as decreased expression of IL-18 BP and increased expression of IL-17. This disregulation allows T cell responses to weakly antigenic CII determinants to progress, thus promoting the development of autoimmune arthritis.

DOI

10.21007/etd.cghs.2009.0159

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