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A defect in tryptophan catabolism impairs tolerance in nonobese diabetic mice.

Grohmann U, Fallarino F, Bianchi R, Orabona C, Vacca C, Fioretti MC, Puccetti P - J. Exp. Med. (2003)

Bottom Line: This cytokine may be instrumental in specific forms of tolerance by virtue of its ability to activate immunosuppressive tryptophan catabolism.This effect is associated with impaired tryptophan catabolism, is related to transient blockade of the Stat1 pathway of intracellular signaling by IFN-gamma, and is caused by peroxynitrite production.This is the first report of an experimental autoimmune disease in which defective tolerance is causally linked to impaired tryptophan catabolism.

View Article: PubMed Central - PubMed

Affiliation: Department of Experimental Medicine, University of Perugia, 06126 Perugia, Italy. ugrohmann@tin.it

ABSTRACT
The predisposition of nonobese diabetic (NOD) mice to develop autoimmunity reflects deficiencies in both peripheral and central tolerance. Several defects have been described in these mice, among which aberrant antigen-presenting cell function and peroxynitrite formation. Prediabetes and diabetes in NOD mice have been targeted with different outcomes by a variety of immunotherapies, including interferon (IFN)-gamma. This cytokine may be instrumental in specific forms of tolerance by virtue of its ability to activate immunosuppressive tryptophan catabolism. Here, we provide evidence that IFN-gamma fails to induce tolerizing properties in dendritic cells from highly susceptible female mice early in prediabetes. This effect is associated with impaired tryptophan catabolism, is related to transient blockade of the Stat1 pathway of intracellular signaling by IFN-gamma, and is caused by peroxynitrite production. However, the use of a peroxynitrite inhibitor can rescue tryptophan catabolism and tolerance in those mice. This is the first report of an experimental autoimmune disease in which defective tolerance is causally linked to impaired tryptophan catabolism.

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CD8+ DCs from early prediabetic NOD female mice are not activated by IFN-γ to suppress NRP-A7 priming by CD8− DCs. Induction of skin test reactivity to NRP-A7 was studied in 4-wk-old hosts transferred with DC subtypes with or without cytokine treatment. DCs from 8- or 4-wk-old mice were fractionated according to CD8 expression and were used as such (CD8−, CD8+) or after treatment with IL-12 (CD8−/IL-12) or IFN-γ (CD8+/IFN-γ). After peptide pulsing, the different fractions were injected either singly or in combination (indicated). Experimental groups included the use of CD8+ DCs treated with 2 μM 1-MT during exposure to IFN-γ. (*) P < 0.001, experimental versus control footpads. ND, not done. One experiment is reported representative of five.
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fig1: CD8+ DCs from early prediabetic NOD female mice are not activated by IFN-γ to suppress NRP-A7 priming by CD8− DCs. Induction of skin test reactivity to NRP-A7 was studied in 4-wk-old hosts transferred with DC subtypes with or without cytokine treatment. DCs from 8- or 4-wk-old mice were fractionated according to CD8 expression and were used as such (CD8−, CD8+) or after treatment with IL-12 (CD8−/IL-12) or IFN-γ (CD8+/IFN-γ). After peptide pulsing, the different fractions were injected either singly or in combination (indicated). Experimental groups included the use of CD8+ DCs treated with 2 μM 1-MT during exposure to IFN-γ. (*) P < 0.001, experimental versus control footpads. ND, not done. One experiment is reported representative of five.

Mentions: NRP-A7 is a synthetic nonapeptide that elicits the proliferation, cytokine secretion, differentiation, and cytotoxicity of a diabetogenic H-2Kd–restricted CD8+ T cell specificity that uses a TCRα rearrangement frequently expressed by CD8+ T cells propagated from the earliest insulitic lesions of NOD mice (14, 15). Cell populations in the spleens of conventional strains of mice contain variable proportions of mature CD8− and CD8+ DCs that mediate the respective immunogenic and tolerogenic presentation of NRP-A7. Upon transfer into recipient hosts, peptide-loaded CD8− DCs initiate immunity, and CD8+ DCs initiate anergy, when antigen-specific skin test reactivity is measured at 2 wk after cell transfer. The addition of as few as 3% CD8+ DCs to a population of CD8− DCs inhibits priming by the latter cells in this model of class I–restricted reactivity to the synthetic peptide (13, 17). We examined CD8− and CD8+ DCs from NOD mice for their patterns of presentation of NRP-A7 in vivo. Female mice of two different ages, 4 and 8 wk, were used as a source of splenic DCs that were fractionated, loaded with the peptide, and injected into recipient hosts to be assayed at 2 wk for NRP-A7-specific skin test reactivity. CD8− DCs were injected either alone or in combination with 3% CD8+ DCs, and each subset was used either as such or after exposure to IL-12 (for CD8− DCs) or IFN-γ (for CD8+ DCs; Fig. 1). Presentation by CD8− DCs resulted in effective priming, which effect was negated by the copresence of CD8+ DCs in the cell transfer. Similar to what observed in conventional mice (16), the suppressive effect of IFN-γ prevailed over the adjuvant activity of IL-12 acting on CD8− DCs when 8-wk-old mice were used as a source of DCs. The effect of IFN-γ was dependent upon effective tryptophan catabolism, as it was ablated by the addition of the IDO enzyme inhibitor, 1-MT, during CD8+ DC exposure to the cytokine. In contrast, IFN-γ was completely unable to induce suppressive properties in CD8+ DCs from 4-wk-old mice and thus overcome the stimulatory activity of IL-12. In experiments not reported here using male mice, we found that IFN-γ acted equally well in CD8+ DCs from donors of 4 or 8 wk of age. Thus, CD8+ DCs from early prediabetic female mice are characterized by specific unresponsiveness to modulation of activity by IFN-γ and by inability to counter the adjuvant activity of IL-12 acting on CD8− DCs.


A defect in tryptophan catabolism impairs tolerance in nonobese diabetic mice.

Grohmann U, Fallarino F, Bianchi R, Orabona C, Vacca C, Fioretti MC, Puccetti P - J. Exp. Med. (2003)

CD8+ DCs from early prediabetic NOD female mice are not activated by IFN-γ to suppress NRP-A7 priming by CD8− DCs. Induction of skin test reactivity to NRP-A7 was studied in 4-wk-old hosts transferred with DC subtypes with or without cytokine treatment. DCs from 8- or 4-wk-old mice were fractionated according to CD8 expression and were used as such (CD8−, CD8+) or after treatment with IL-12 (CD8−/IL-12) or IFN-γ (CD8+/IFN-γ). After peptide pulsing, the different fractions were injected either singly or in combination (indicated). Experimental groups included the use of CD8+ DCs treated with 2 μM 1-MT during exposure to IFN-γ. (*) P < 0.001, experimental versus control footpads. ND, not done. One experiment is reported representative of five.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2196078&req=5

fig1: CD8+ DCs from early prediabetic NOD female mice are not activated by IFN-γ to suppress NRP-A7 priming by CD8− DCs. Induction of skin test reactivity to NRP-A7 was studied in 4-wk-old hosts transferred with DC subtypes with or without cytokine treatment. DCs from 8- or 4-wk-old mice were fractionated according to CD8 expression and were used as such (CD8−, CD8+) or after treatment with IL-12 (CD8−/IL-12) or IFN-γ (CD8+/IFN-γ). After peptide pulsing, the different fractions were injected either singly or in combination (indicated). Experimental groups included the use of CD8+ DCs treated with 2 μM 1-MT during exposure to IFN-γ. (*) P < 0.001, experimental versus control footpads. ND, not done. One experiment is reported representative of five.
Mentions: NRP-A7 is a synthetic nonapeptide that elicits the proliferation, cytokine secretion, differentiation, and cytotoxicity of a diabetogenic H-2Kd–restricted CD8+ T cell specificity that uses a TCRα rearrangement frequently expressed by CD8+ T cells propagated from the earliest insulitic lesions of NOD mice (14, 15). Cell populations in the spleens of conventional strains of mice contain variable proportions of mature CD8− and CD8+ DCs that mediate the respective immunogenic and tolerogenic presentation of NRP-A7. Upon transfer into recipient hosts, peptide-loaded CD8− DCs initiate immunity, and CD8+ DCs initiate anergy, when antigen-specific skin test reactivity is measured at 2 wk after cell transfer. The addition of as few as 3% CD8+ DCs to a population of CD8− DCs inhibits priming by the latter cells in this model of class I–restricted reactivity to the synthetic peptide (13, 17). We examined CD8− and CD8+ DCs from NOD mice for their patterns of presentation of NRP-A7 in vivo. Female mice of two different ages, 4 and 8 wk, were used as a source of splenic DCs that were fractionated, loaded with the peptide, and injected into recipient hosts to be assayed at 2 wk for NRP-A7-specific skin test reactivity. CD8− DCs were injected either alone or in combination with 3% CD8+ DCs, and each subset was used either as such or after exposure to IL-12 (for CD8− DCs) or IFN-γ (for CD8+ DCs; Fig. 1). Presentation by CD8− DCs resulted in effective priming, which effect was negated by the copresence of CD8+ DCs in the cell transfer. Similar to what observed in conventional mice (16), the suppressive effect of IFN-γ prevailed over the adjuvant activity of IL-12 acting on CD8− DCs when 8-wk-old mice were used as a source of DCs. The effect of IFN-γ was dependent upon effective tryptophan catabolism, as it was ablated by the addition of the IDO enzyme inhibitor, 1-MT, during CD8+ DC exposure to the cytokine. In contrast, IFN-γ was completely unable to induce suppressive properties in CD8+ DCs from 4-wk-old mice and thus overcome the stimulatory activity of IL-12. In experiments not reported here using male mice, we found that IFN-γ acted equally well in CD8+ DCs from donors of 4 or 8 wk of age. Thus, CD8+ DCs from early prediabetic female mice are characterized by specific unresponsiveness to modulation of activity by IFN-γ and by inability to counter the adjuvant activity of IL-12 acting on CD8− DCs.

Bottom Line: This cytokine may be instrumental in specific forms of tolerance by virtue of its ability to activate immunosuppressive tryptophan catabolism.This effect is associated with impaired tryptophan catabolism, is related to transient blockade of the Stat1 pathway of intracellular signaling by IFN-gamma, and is caused by peroxynitrite production.This is the first report of an experimental autoimmune disease in which defective tolerance is causally linked to impaired tryptophan catabolism.

View Article: PubMed Central - PubMed

Affiliation: Department of Experimental Medicine, University of Perugia, 06126 Perugia, Italy. ugrohmann@tin.it

ABSTRACT
The predisposition of nonobese diabetic (NOD) mice to develop autoimmunity reflects deficiencies in both peripheral and central tolerance. Several defects have been described in these mice, among which aberrant antigen-presenting cell function and peroxynitrite formation. Prediabetes and diabetes in NOD mice have been targeted with different outcomes by a variety of immunotherapies, including interferon (IFN)-gamma. This cytokine may be instrumental in specific forms of tolerance by virtue of its ability to activate immunosuppressive tryptophan catabolism. Here, we provide evidence that IFN-gamma fails to induce tolerizing properties in dendritic cells from highly susceptible female mice early in prediabetes. This effect is associated with impaired tryptophan catabolism, is related to transient blockade of the Stat1 pathway of intracellular signaling by IFN-gamma, and is caused by peroxynitrite production. However, the use of a peroxynitrite inhibitor can rescue tryptophan catabolism and tolerance in those mice. This is the first report of an experimental autoimmune disease in which defective tolerance is causally linked to impaired tryptophan catabolism.

Show MeSH
Related in: MedlinePlus