T cells with low avidity for a tissue-restricted antigen routinely evade central and peripheral tolerance and cause autoimmunity

Abstract

T cells causing autoimmunity must escape tolerance. We observed that CD8(+) T cells with high avidity for an antigen expressed in the pancreas, kidney, and thymic medulla were efficiently removed from a polyclonal repertoire by central and peripheral tolerance mechanisms. However, both mechanisms spared low-avidity T cells from elimination. Neither the introduction of activated, self-antigen-specific CD4(+) helper T cells nor a global inflammatory stimulus were sufficient to activate the low-avidity CD8(+) T cells and did not break tolerance. In contrast, challenge with a recombinant bacterium expressing the self antigen primed the low-avidity T cells, and the animals rapidly developed autoimmune diabetes. We suggest that whereas thymic and peripheral tolerance mechanisms remove cells that can be primed by endogenous amounts of self antigen, they do not guard against tissue destruction by low-avidity effector T cells, which have been primed by higher amounts of self antigen or by crossreactive antigens.

Figure 1

Tetramer Staining of Naive B6, Vβ5, and Vβ5×Rip-mOva (C) Mice Peripheral blood cells from B6 (A), Vβ5 (B), and Vβ5×Rip-mOva (C) mice were stained with anti-CD8 and K^b-Ova tetramer. The representative plots shown are gated on CD8⁺ T cells. The regions highlight cells staining at high and low levels with tetramer, and the numbers represent their frequency within the CD8⁺ T cell population. The data are representative of three independent experiments.

Figure 2

Detection of K^b-Ova-Reactive T Cells in Nonimmunized Mice (A) Peripheral blood CD8⁺ T cells from OT-I, Vβ5, Vβ5×Rip-mOva, and control B6 mice were expanded with anti-CD3 plus anti-CD28 beads. 6 days later, cells were stimulated with congenically marked splenocytes in the presence of PMA and Ionomycin, no peptide, or the indicated concentrations of Ova_257-264 peptide and analyzed for intracellular accumulation of IFNγ. Representative flow data gated on expanded CD8⁺ T cells are shown. (B and C) Peptide dose-response curves graphing the mean percentage of peripheral blood CD8⁺ T cells in Vβ5×Rip-mOva, Vβ5, and B6 (B) or of CD8⁺ T cells isolated from pancreatic lymph nodes of Vβ5×Rip-mOva and Vβ5 mice (C) that specifically produce IFNγ in response to Ova_257-264 stimulation. Bars represent standard deviation of data from 3–5 mice. Results are representative of at least three experiments.

Figure 3

Incidence of Autoimmune Diabetes in Vβ5×Rip-mOva Mice after Lm-Ova Infection Vβ5×Rip-mOva mice were immunized with Listeria monocytogenes-expressing ovalbumin (Lm-Ova) or wild-type Listeria (Lm-wt). Blood glucose was monitored starting from day 5–7 until day 11 postinfection, and mice with levels above 300 mg/dl were considered diabetic. (A) Maximum blood glucose levels, detected between days 5–6 and days 7–9 post Lm-Ova (triangles) infection and days 7–9 after Lm-wt (squares) infection are shown. (B) Representative 20× magnified, HE-stained pancreas sections of Lm-Ova-immunized Vβ5×Rip-mOva (left) and Vβ5 (middle) mice and Lm-wt-immunized Vβ5×Rip-mOva mice (right) are presented.

Figure 4

Comparison of Functional Avidity of K^b-Ova-Reactive T Cells Found after Lm-Ova Infection in Vβ5×Rip-mOva and Vβ5 Mice (A) Splenocytes harvested from Vβ5×Rip-mOva (n = 4) and Vβ5 (n = 6) mice on day 7 post Lm-Ova infection and from unimmunized Vβ5×Rip-mOva (n = 1) and Vβ5 (n = 1) mice were stimulated with the indicated concentrations of Ova peptide and analyzed for the percentage of CD8⁺ T cells producing IFNγ. The mean percentage of CD8⁺ T cells producing IFNγ is graphed against the concentration of Ova peptide used to stimulate the cells (error bars represent standard deviation). (B) Comparison of the functional avidity of Ova peptide-reactive T cells found on day 7 post Lm-Ova infection in the pancreas (n = 1), pancreatic lymph nodes (n = 1), and spleen (n = 4) of Vβ5×Rip-mOva mice and in the spleen of immunized Vβ5 mice (n = 6). The extent of IFNγ production at a given peptide concentration is shown as the fraction of the responses induced by 10⁻⁵ M peptide. Data for splenocytes is derived from (A). Pancreas infiltrating and pancreatic lymph node CD8⁺ T cells were expanded with anti-CD3 plus anti-CD28 for 6 days, then stimulated with congenically marked splenocytes plus Ova peptide and analyzed for IFNγ production. Shown are mean values for the indicated number of mice used, and where applicable bars represent standard deviation.

Figure 5

Influence of Central and Peripheral Tolerance on CD8⁺ T Cells Reactive to a Tissue-Restricted Antigen (A) Thymocytes from 9-week-old Vβ5×Rip-mOva (n = 3) and Vβ5 (n = 3) mice were adoptively transferred into Rag1^−/− mice at a ratio of one thymus per recipient. 24 hr later, the mice were infected with Lm-Ova, and 7 days after infection, splenocytes were harvested and analyzed for CD8⁺ T cells producing IFNγ in response to Ova peptide. The flow cytometry plots are representative of cells stimulated with 10⁻¹⁰ M Ova or no peptide control. The graph shows the complete peptide titration. Bars represent standard deviation of three mice. (B) 10⁷ splenic Ly5.1 CD8⁺ T cells from Vβ5 mice were adoptively transferred either into Rip-mOva (Ly5.2) transgenic mice (n = 2) or into control B6 (Ly5.2) mice (n = 2). 6 weeks later, grafted T cells were reisolated from the host spleen and expanded for 6 days with anti-CD3 plus anti-CD28 beads. After stimulation with Ova peptide-pulsed splenocytes (Ly5.2), the expanded cells were analyzed for intracellular IFNγ. The flow plots gated on Ly5.1 cells show representative stains for stimulation with 10⁻¹⁰ M Ova or no peptide control, and the complete titration curve for the donor cells is shown in the graph. Shown are mean values for the indicated number of mice and the bars represent the position of individual data points. The results are representative of at least two experiments.