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Competition between two MHC binding registers in a single peptide processed from myelin basic protein influences tolerance and susceptibility to autoimmunity.

Seamons A, Sutton J, Bai D, Baird E, Bonn N, Kafsack BF, Shabanowitz J, Hunt DF, Beeson C, Goverman J - J. Exp. Med. (2003)

Bottom Line: The results demonstrate that competition between two I-Au binding registers, a low affinity register defined by MBPAc1-11 and a high affinity register defined by MBP5-16, prevents most of the NH2-terminal naturally processed peptides from binding in the MBPAc1-11 register.The small fraction of MBPAc1-18 bound in the MBPAc1-11 register is not sufficient to induce tolerance but provides a ligand for MBPAc1-11-specific T cells during disease.These results provide a basis for both the lack of tolerance to MBPAc1-11 and the ability of this epitope to become a target during autoimmunity.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology, Box 357650, University of Washington, Seattle, WA 98195, USA.

ABSTRACT
Experimental allergic encephalomyelitis (EAE) is an animal model for multiple sclerosis induced by stimulating myelin basic protein (MBP)-specific T cells. The MBP-specific repertoire in B10.PL mice is shaped by tolerance mechanisms that eliminate MBP121-150-specific T cells. In contrast, MBPAc1-11-specific T cells escape tolerance and constitute the encephalitogenic repertoire. To determine if this differential tolerance is caused by differences in the abundance of MBP epitopes generated by processing, MBP peptides were eluted from I-Au complexes and analyzed by mass spectrometry. Peptides were identified from both the NH2-terminal and MBP121-150 regions. Unexpectedly, MBPAc1-18 and Ac1-17, which contain the MBPAc1-11 epitope, were much more abundant than MBP121-150 peptides. The results demonstrate that competition between two I-Au binding registers, a low affinity register defined by MBPAc1-11 and a high affinity register defined by MBP5-16, prevents most of the NH2-terminal naturally processed peptides from binding in the MBPAc1-11 register. The small fraction of MBPAc1-18 bound in the MBPAc1-11 register is not sufficient to induce tolerance but provides a ligand for MBPAc1-11-specific T cells during disease. These results provide a basis for both the lack of tolerance to MBPAc1-11 and the ability of this epitope to become a target during autoimmunity.

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MBPAc1–18 demonstrates biphasic dissociation. (A) Dissociation of fluorescein-labeled MBP peptides from soluble I-Au. MBP peptides were incubated with soluble I-Au for 1 h at 37°C. For MBPAc1–18, ∼38% of the original peptide bound was bound in the faster phase: t1/2fast = 3.7 h. About 62% of the initial peptide is bound in the slow phase: t1/2slow = 117 h. (B) Expanded time scale of panel A showing the monophasic fast dissociation of both MBPAc1–18Y12A and MBPAc1–11.
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fig2: MBPAc1–18 demonstrates biphasic dissociation. (A) Dissociation of fluorescein-labeled MBP peptides from soluble I-Au. MBP peptides were incubated with soluble I-Au for 1 h at 37°C. For MBPAc1–18, ∼38% of the original peptide bound was bound in the faster phase: t1/2fast = 3.7 h. About 62% of the initial peptide is bound in the slow phase: t1/2slow = 117 h. (B) Expanded time scale of panel A showing the monophasic fast dissociation of both MBPAc1–18Y12A and MBPAc1–11.

Mentions: We investigated whether the NH2-terminal peptides could bind I-Au using both binding registers by analyzing the dissociation kinetics of MBPAc1–18 as well as smaller peptides representing the individual binding registers from solubilized I-Au. MBP5–16/I-Au dissociated so slowly that a half-life was difficult to measure (t1/2 > 1,000 h). The half-life of MBPAc1–11/I-Au was only 30 min. Interestingly, MBPAc1–18/I-Au dissociated with biphasic kinetics, suggesting that the peptide binds in a mixture of short-lived and long-lived complexes (Fig. 2 A). Under these binding conditions (incubation with MHC molecules for 1 h at 37°C), ∼38% and 62% of the MBPAc1–18 peptides formed short- and long-lived complexes, respectively. Increasing the incubation time from 1 to 16 h increased the amount of MBPAc1–18 peptide bound in the long phase to 77% (unpublished data). Dissociation of analogue peptides with mutations in the p6 anchor residues for each register was also analyzed. The MBPAc1–18Y12A substitution, which abrogates binding in the MBP5–16 register, exhibits single phase, rapid dissociation essentially identical to the dissociation of MBPAc1–11 (Fig. 2, A and B). Conversely, the MBPAc1–18K4Y substitution, which replaces the unfavorable lysine with a tyrosine in the anchor position of the MBPAc1–11 register, exhibits single phase, slow-dissociation kinetics with a half-life very similar to the slow-dissociation phase of native MBPAc1–18 (Fig. 2 A). These data confirm the utilization of two binding registers within MBPAc1–18 and suggest that most, but not all, of MBPAc1–18 is bound to I-Au in the MBP5–16 register.


Competition between two MHC binding registers in a single peptide processed from myelin basic protein influences tolerance and susceptibility to autoimmunity.

Seamons A, Sutton J, Bai D, Baird E, Bonn N, Kafsack BF, Shabanowitz J, Hunt DF, Beeson C, Goverman J - J. Exp. Med. (2003)

MBPAc1–18 demonstrates biphasic dissociation. (A) Dissociation of fluorescein-labeled MBP peptides from soluble I-Au. MBP peptides were incubated with soluble I-Au for 1 h at 37°C. For MBPAc1–18, ∼38% of the original peptide bound was bound in the faster phase: t1/2fast = 3.7 h. About 62% of the initial peptide is bound in the slow phase: t1/2slow = 117 h. (B) Expanded time scale of panel A showing the monophasic fast dissociation of both MBPAc1–18Y12A and MBPAc1–11.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2193784&req=5

fig2: MBPAc1–18 demonstrates biphasic dissociation. (A) Dissociation of fluorescein-labeled MBP peptides from soluble I-Au. MBP peptides were incubated with soluble I-Au for 1 h at 37°C. For MBPAc1–18, ∼38% of the original peptide bound was bound in the faster phase: t1/2fast = 3.7 h. About 62% of the initial peptide is bound in the slow phase: t1/2slow = 117 h. (B) Expanded time scale of panel A showing the monophasic fast dissociation of both MBPAc1–18Y12A and MBPAc1–11.
Mentions: We investigated whether the NH2-terminal peptides could bind I-Au using both binding registers by analyzing the dissociation kinetics of MBPAc1–18 as well as smaller peptides representing the individual binding registers from solubilized I-Au. MBP5–16/I-Au dissociated so slowly that a half-life was difficult to measure (t1/2 > 1,000 h). The half-life of MBPAc1–11/I-Au was only 30 min. Interestingly, MBPAc1–18/I-Au dissociated with biphasic kinetics, suggesting that the peptide binds in a mixture of short-lived and long-lived complexes (Fig. 2 A). Under these binding conditions (incubation with MHC molecules for 1 h at 37°C), ∼38% and 62% of the MBPAc1–18 peptides formed short- and long-lived complexes, respectively. Increasing the incubation time from 1 to 16 h increased the amount of MBPAc1–18 peptide bound in the long phase to 77% (unpublished data). Dissociation of analogue peptides with mutations in the p6 anchor residues for each register was also analyzed. The MBPAc1–18Y12A substitution, which abrogates binding in the MBP5–16 register, exhibits single phase, rapid dissociation essentially identical to the dissociation of MBPAc1–11 (Fig. 2, A and B). Conversely, the MBPAc1–18K4Y substitution, which replaces the unfavorable lysine with a tyrosine in the anchor position of the MBPAc1–11 register, exhibits single phase, slow-dissociation kinetics with a half-life very similar to the slow-dissociation phase of native MBPAc1–18 (Fig. 2 A). These data confirm the utilization of two binding registers within MBPAc1–18 and suggest that most, but not all, of MBPAc1–18 is bound to I-Au in the MBP5–16 register.

Bottom Line: The results demonstrate that competition between two I-Au binding registers, a low affinity register defined by MBPAc1-11 and a high affinity register defined by MBP5-16, prevents most of the NH2-terminal naturally processed peptides from binding in the MBPAc1-11 register.The small fraction of MBPAc1-18 bound in the MBPAc1-11 register is not sufficient to induce tolerance but provides a ligand for MBPAc1-11-specific T cells during disease.These results provide a basis for both the lack of tolerance to MBPAc1-11 and the ability of this epitope to become a target during autoimmunity.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology, Box 357650, University of Washington, Seattle, WA 98195, USA.

ABSTRACT
Experimental allergic encephalomyelitis (EAE) is an animal model for multiple sclerosis induced by stimulating myelin basic protein (MBP)-specific T cells. The MBP-specific repertoire in B10.PL mice is shaped by tolerance mechanisms that eliminate MBP121-150-specific T cells. In contrast, MBPAc1-11-specific T cells escape tolerance and constitute the encephalitogenic repertoire. To determine if this differential tolerance is caused by differences in the abundance of MBP epitopes generated by processing, MBP peptides were eluted from I-Au complexes and analyzed by mass spectrometry. Peptides were identified from both the NH2-terminal and MBP121-150 regions. Unexpectedly, MBPAc1-18 and Ac1-17, which contain the MBPAc1-11 epitope, were much more abundant than MBP121-150 peptides. The results demonstrate that competition between two I-Au binding registers, a low affinity register defined by MBPAc1-11 and a high affinity register defined by MBP5-16, prevents most of the NH2-terminal naturally processed peptides from binding in the MBPAc1-11 register. The small fraction of MBPAc1-18 bound in the MBPAc1-11 register is not sufficient to induce tolerance but provides a ligand for MBPAc1-11-specific T cells during disease. These results provide a basis for both the lack of tolerance to MBPAc1-11 and the ability of this epitope to become a target during autoimmunity.

Show MeSH
Related in: MedlinePlus