Helios defines T cells being driven to tolerance in the periphery and thymus.

The expression of the Ikaros transcription factor family member, Helios, has been shown to be associated with T-cell tolerance in both the thymus and the periphery. To better understand the importance of Helios in tolerance pathways, we have examined the expression of Helios in TCR-transgenic T cells specific for the gastric H(+) /K(+) ATPase, the autoantigen target in autoimmune gastritis. Analysis of H(+) /K(+) ATPase-specific T cells in mice with different patterns of H(+) /K(+) ATPase expression revealed that, in addition to the expression of Helios in CD4(+) Foxp3(+) regulatory T (Treg) cells, Helios is expressed by a large proportion of CD4(+) Foxp3(-) T cells in both the thymus and the paragastric lymph node (PgLN), which drains the stomach. In the thymus, Helios was expressed by H(+) /K(+) ATPase-specific thymocytes that were undergoing negative selection. In the periphery, Helios was expressed in H(+) /K(+) ATPase-specific CD4(+) T cells following H(+) /K(+) ATPase presentation and was more highly expressed when T-cell activation occurred in the absence of inflammation. Analysis of purified H(+) /K(+) ATPase-specific CD4(+) Foxp3(-) Helios(+) T cells demonstrated that they were functionally anergic. These results demonstrate that Helios is expressed by thymic and peripheral T cells that are being driven to tolerance in response to a genuine autoantigen.

Both IFN-γ and IL-17 are required for the development of severe autoimmune gastritis.

IL-17, produced by a distinct lineage of CD4(+) helper T (Th) cells termed Th17 cells, induces the production of pro-inflammatory cytokines from resident cells and it has been demonstrated that over-expression of IL-17 plays a crucial role in the onset of several auto-immune diseases. Here we examined the role of IL-17 in the pathogenesis of autoimmune gastritis, a disease that was previously believed to be mediated by IFN-γ. Significantly higher levels of IL-17 and IFN-γ were found in the stomachs and stomach-draining lymph nodes of mice with severe autoimmune gastritis. Unlike IL-17, which was produced solely by CD4(+) T cells in gastritic mice, the majority of IFN-γ-producing cells were CD8(+) T cells. However, CD8(+) T cells alone were not able to induce autoimmune gastritis. T cells that were deficient in IL-17 or IFN-γ production were able to induce autoimmune gastritis but to a much lower extent compared with the disease induced by wild-type T cells. These data demonstrate that production of neither IL-17 nor IFN-γ by effector T cells is essential for the initiation of autoimmune gastritis, but suggest that both are required for the disease to progress to the late pathogenic stage that includes significant tissue disruption.

A convenient model of severe, high incidence autoimmune gastritis caused by polyclonal effector T cells and without perturbation of regulatory T cells.

Autoimmune gastritis results from the breakdown of T cell tolerance to the gastric H(+)/K(+) ATPase. The gastric H(+)/K(+) ATPase is responsible for the acidification of gastric juice and consists of an α subunit (H/Kα) and a ß subunit (H/Kß). Here we show that CD4(+) T cells from H/Kα-deficient mice (H/Kα(-/-)) are highly pathogenic and autoimmune gastritis can be induced in sublethally irradiated wildtype mice by adoptive transfer of unfractionated CD4(+) T cells from H/Kα(-/-) mice. All recipient mice consistently developed the most severe form of autoimmune gastritis 8 weeks after the transfer, featuring hypertrophy of the gastric mucosa, complete depletion of the parietal and zymogenic cells, and presence of autoantibodies to H(+)/K(+) ATPase in the serum. Furthermore, we demonstrated that the disease significantly affected stomach weight and stomach pH of recipient mice. Depletion of parietal cells in this disease model required the presence of both H/Kα and H/Kß since transfer of H/Kα(-/-) CD4(+) T cells did not result in depletion of parietal cells in H/Kα(-/-) or H/Kß(-/-) recipient mice. The consistency of disease severity, the use of polyclonal T cells and a specific T cell response to the gastric autoantigen make this an ideal disease model for the study of many aspects of organ-specific autoimmunity including prevention and treatment of the disease.

Extrathymic mechanisms of T cell tolerance: lessons from autoimmune gastritis.

While the thymus plays a key role in the prevention of many autoimmune phenomena it is clear that robust mechanisms external to the thymus are also vital in controlling self-reactive T cells. Here we review the current concepts in the field of extrathymic tolerance and use recent studies of autoimmune gastritis to illustrate how T cells directed to a prominent, clinically relevant autoantigen, namely the gastric proton pump, can be silenced with little or no thymic involvement. Autoimmune gastritis represents one of the most thoroughly characterised autoimmune systems and the knowledge and tools available to study this disease will continue to allow a thorough assessment of the genetic, cellular and molecular events that underlie tolerance and autoimmunity.

Prevention of autoimmune gastritis in mice requires extra-thymic T-cell deletion and suppression by regulatory T cells.

BACKGROUND AND AIMS: Autoimmune gastritis is one of the most common autoimmune diseases and is caused by a CD4(+) T-cell response to the gastric H(+)/K(+) ATPase encoded by Atp4a and Atp4b (H(+)/K(+) ATPase). Here, we have elucidated events that result in immunological tolerance to the H(+)/K(+) ATPase and thus the prevention of autoimmune gastritis. METHODS: T cells from H(+)/K(+) ATPase-deficient mice and H(+)/K(+) ATPase-specific T-cell receptor transgenic mice were purified and transferred to wild-type (WT) or H(+)/K(+) ATPase-deficient recipients to assess the impact of exposure to antigen on pathogenicity. RESULTS: The CD4(+) T-cell population from H(+)/K(+) ATPase-deficient mice was highly effective at inducing gastritis when compared with T cells from WT mice and, as a population, was comparatively resistant to the suppressive activity of regulatory T cells. Exposing T cells from H(+)/K(+) ATPase-deficient mice to H(+)/K(+) ATPase in WT mice decreased their ability to induce gastritis and resulted in a population that could be more easily suppressed by T(reg) cells. Transfer of clonotypic antigen-inexperienced H(+)/K(+) ATPase-specific T cells into WT mice resulted in extra-thymic clonal deletion. CONCLUSIONS: Prevention of autoimmune gastritis requires the extra-thymic purging of highly autoaggressive H(+)/K(+) ATPase-specific T cells to produce a T-cell repertoire that is more susceptible to the suppressive activity of regulatory T cells. Taken together with recent published data describing the role of T-cell receptor signalling in the maintenance of regulatory T-cell populations, we propose that exposure of T cells to antigen in the periphery is able to both delete autoaggressive specificities and maintain regulatory T-cell activity, establishing a balance between pathogenicity and regulation.