Doctoral Dissertations

Booki Min

Date of Award

5-2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Microbiology

Major Professor

Habib Zaghouani

Committee Members

Robert N. Moore, Rouse, Saluson

Abstract

During T cell development within the thymus the immune system has developed several regulatory checkpoints to ensure the elimination of T cells endowed with antigen receptors specific for self antigens. Although such a tight regulation exists, some autoreactive T cells escape and undergo the maturation process. The activation of those autoreactive T cells leads to the development of autoimmune diseases.

The neonatal period has been considered as a window during which the encounter with antigens instructs not to develop immune responses, but rather, induces tolerance. Therefore, introduction with defined autoantigens into neonates could be an attractive strategy to induce neonatal tolerance, preventing the development of autoimmunity. The necessity of incomplete Freund's adjuvant (IFA), however, hampers its clinical application.

It has been shown that immunoglobulin (Ig) can be used as an antigenic delivery system, and such delivery was efficient by increasing peptide presentation by 100-1000 fold. Furthermore, Igs are persistent for a long time in vivo. Herein, we hypothesized that Ig-mediated peptide delivery into neonates may replace the requirement of IFA, thereby inducing neonatal tolerance.

Following the introductory literature overview, part II describes the expression of a dominant encephalitogenic peptide (PLP 139-151, PLP1) derived from proteolipid protein (PLP) in place of CDR3 region of Ig molecule. PLP is a known autoantigen for experimental allergic encephalomyelitis (EAE), an animal model for human multiple sclerosis (MS). The results indicate that the peptide was incorporated into the variable region in a correct reading frame. Furthermore, peptide presentation by chimeric Ig molecule was antigen specific and had great efficiency in T cell stimulation by 100-1000 fold.

In the following part III it was shown that neonatal injection with resulting Ig- PLP1 conferred a resistance to EAE without the presence of IFAThe mechanism underlying such resistance included IL-4-driven lymph node deviation, and IFNYγdependent splenic anergy restorable by exogenous IFNγ or IL-12.

Part IV showed that neonatal tolerance induced by Ig-PLP1 was unique and differentially regulated by the dose of antigen, the presence of adjuvant, and the number of injectionsThe results indicate that the dose of Ig-PLP1 displayed a quantitative variation in the outcome of tolerance, whereas adjuvant and the number of injections had a rather qualitative effect on the neonatal tolerance.

Part V demonstrated the cellular mechanism for splenic T cell anergyThe results show that splenic cells from Ig-PLP1 tolerized mice displayed an anergic phenotype by the inability to upregulate IL-2 receptor a chain (CD25), which is responsible for responsiveness to IL-2. Furthermore, this defect in CD25 expression by splenic cells was shown to be critical in order to maintain long-lasting persistence of Ig-PLP1 mediated tolerance.

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