Title

Autoimmunity and tolerance to intestinal protein

Date of Completion

January 2002

Keywords

Health Sciences, Immunology

Degree

Ph.D.

Abstract

Antigen-specific immune responses to self-antigens of intestinal origin have not been thoroughly studied. A transgenic mouse (232) producing a non-secreted, cytoplasmic form of ovalbumin (ova) exclusively in small intestinal enterocytes was employed to address the impact of such protein on T cells. Adoptive transfer of naïve OT-I cells, CD8 T cells recognizing ova, to these mice revealed the presence of cross-presented antigen in gut-draining lymphoid structures. The cognate interaction of T cells with self-antigen led to proliferation, effector function induction and migration to all areas of the body. Large numbers of these cells were found in the epithelial layer of the intestine, but no tissue damage was evident. However, infection of mice with virus making ova (VSV-ova) at the time of cell transfer induced malaise and tissue damage often resulting in death. This CD8 T cell mediated auto-aggressiveness was dependent on Fas engagement, as well as lymphotoxin-β secretion. No role for perforin in intestinal tissue destruction was noted. The inclusion of non-antigenic forms of inflammation, such as wild-type VSV, oral cholera toxin or CD40 triggering, changed the tolerogenic response to one inducing tissue damage. This indicated that products from infectious organisms can combine with self-antigen to shift CD8 T cell responses towards autoimmunity. The impact of this self-antigen on the endogenous T cell repertoire was assessed in transgenic mice via MHC class I tetramer usage, as well as ELISPOT technology. Although no CD8 T cells were detected via tetramers complexed to ova after VSV-ova infection, functional ova-specific CD8 T cells were present based on interferon-γ and IL-4 secretion. This was also true for ova-specific CD4 T cells. The 232 animals had a response shifted towards IL-4 production, as compared to an interferon-γ dominant response in non-transgenic B6 animals. The same skewing was seen in responses to VSV proteins, indicating the presence of memory regulatory cells in 232 mice which impact on the priming of T cells to novel epitopes. The 232 mice were tolerant to ova after infection, since no tissue damage was noted. However, airway hyper-responsiveness was noted in infected 232 mice, indicating a functional consequence of tolerance. ^