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HLA DRB4 0101-restricted immunodominant T cell autoepitope of pyruvate dehydrogenase complex in primary biliary cirrhosis: evidence of molecular mimicry in human autoimmune diseases.

We established six T cell clones specific for pyruvate dehydrogenase complex (PDC)-E2 peptides from four different patients with primary biliary cirrhosis using 33 different peptides of 17-20 amino acid residues corresponding to human PDC-E2 as stimulating antigens. The minimal T cell epitopes of these six T cell clones were all mapped to the same region of the PDC-E2 peptide 163-176 (GDLLAEIETDKATI), which corresponds to the inner lipoyl domain of PDC-E2. The HLA restriction molecules for this epitope were all identified as HLA DRB4 0101. The common essential amino acids of this epitope for these T cell clones were E, D, and K at positions 170, 172, and 173, respectively; other crucial amino acids for this epitope differed in each T cell clone. In addition, the alanine-substituted peptides at positions 170 and 173, but not 172, inhibited the proliferation of all T cell clones induced by the original peptide of human PDC-E2 163-176, indicating that amino acid D at position 172 is a critical MHC-binding site for all T cell clones tested. Interestingly, all T cell clones reacted to PDC-E2 peptide 36-49 (GDLIAEVETDKATV), which corresponds to the outer lipoyl domain of human PDC-E2. Furthermore, one T cell clone cross-reacted with exogenous antigens such as Escherichia coli PDC-E2 peptide 31- 44/134-147/235-248 (EQSLITVEGDKASM), which has an EXDK sequence. This is a definite demonstration of the presence of molecular mimicry at the T cell clonal level in human autoimmune diseases. It is also considered possible to design peptide-specific immunotherapy based on the findings of T cell autoepitopes in primary biliary cirrhosis.


Summary
We established six T cell clones specific for pyruvate dehydrogenase complex (PDC)-E2 peptides from four different patients with primary biliary cirrhosis using 33 different peptides of [17][18][19][20] amino acid residues corresponding to human PDC-E2 as stimulating antigens. The minimal T cell epitopes of these six T cell clones were all mapped to the same region of the PDC-E2 peptide 163-176 (GDLLAEIETDKATI), which corresponds to the inner lipoyl domain of PDC-E2. The HLA restriction molecules for this epitope were all identified as HLA DRB4 0101. The common essential amino acids of this epitope for these T cell clones were E, D, and K at positions 170, 172, and 173, respectively; other crucial amino acids for this epitope differed in each T cell clone. In addition, the alanine-substituted peptides at positions 170 and 173, but not 172, inhibited the proliferation of all T cell clones induced by the original peptide of human PDC~E2 163-176, indicating that amino acid D at position 172 is a critical MHC~binding site for all T cell clones tested. Interestingly, all T cell clones reacted to PDC-E2 peptide [36][37][38][39][40][41][42][43][44][45][46][47][48][49], which corresponds to the outer lipoyl domain of human PDC-E2. Furthermore, one T cell clone cross-reacted with exogenous antigens such as Escherichia coli PDC-E2 peptide 31-44/134-147/235-248 (EQSLITVEGDKASM), which has an EXDK sequence. This is a definite demonstration of the presence of molecular mimicry at the T cell clonal level in human autoimmune diseases. It is also considered possible to design peptide-specific immunotherapy based on the findings of T cell autoepitopes in primary biliary cirrhosis. p rimary biliary cirrhosis (PBC) 1 is an autoimmune chronic cholestatic liver disease characterized by the presence of antimitochondrial antibodies (AMAs) and inflammation of interlobular bile ducts in the liver (1). PBC affects mainly women and ultimately leads to liver failure (2). The major mitochondrial antigens (Ags) recognized by AMAs have recently been identified as E2 components of 2-oxo acid dehydrogenase complexes; pyruvate dehydrogenase complex (PDC), 2-oxoglutarate dehydrogenase complex (OGDC), and branched chain 2-oxo acid dehydrogenase complex (BCO-ADC) that are localized in the mitochondrial inner membrane (3)(4)(5)(6)(7)(8)(9). Immunohistochemical examinations of the lymphocytes infiltrating the portal tracts of livers of PBC patients 1 Abhreviations used in this paper: Ag, antigen; APC, antigen-presenting cell; AMA, antimitochondrial antibody; BCOADC, branched chain 2-oxo acid dehydrogenase complex; OGDC, 2-oxoglutarate dehydrogenase complex; PBC, primary biliary cirrhosis; PDC, pyruvate dehydrogenase complex; PDC-E2, E2 component of PDC; SI, stimulation index; SP, synthetic peptide. revealed a predominance of activated CD8 § T cells, as well as CD4 + T cells, with B and NK cells (10)(11)(12). By fluorescence microscopy, it has been demonstrated that large amount of Ags immunoreactive with AMAs are present on the surface of biliary epithelial cells in the livers of PBC patients (13)(14)(15). Furthermore, bile duct epithelia and hepatocytes in PBC express large amounts of HLA class I and II molecules (15)(16)(17). These observations suggest that T cell-mediated mechanisms are involved in the pathogenesis of the destruction of bile duct epithelia and hepatocytes in PBC. However, thus far little has been reported on the autoepitopes of the mitochondrial Ags recognized by T cells in PBC (14,(18)(19)(20).
In other human organ-specific autoimmune diseases, such as multiple sclerosis (21)(22)(23)(24), chronic thyroiditis (25)(26)(27)(28), and myasthenia gravis (29)(30)(31)(32), pathogenic T cell autoepitopes and their restriction molecules of MHC class I or II have recently been studied at the molecular level, and some pathogenic T cell autoepitopes have been identified. However, T cell autoepitopes remain to be elucidated in most other autoimmune diseases, because of the methodological limitations in generating stable T cell clones specific for disease-relevant self Ags. Only some primitive studies concerning the T cell autoepitopes of U1 small nuclear ribonucleoprotein A protein (33) and glutamic acid decarboxylase (34,35) have been previously reported for SLE and insulin-dependent diabetes mellitus, respectively.
In the present study, we established six T cell clones specific for PDC-E2 from the peripheral blood of patient s with PBC. Surprisingly, the minimal T cell epitopes of these T cell clones from four different patients with PBC were all mapped to the same region of PDC-E2 peptide 163-176, which corresponds to the inner lipoyl domain of human PDC-E2. Furthermore, all T cell clones were restricted by HLA DRB4 0101. We also found that there are three common essential amino acid residues for this epitope, EXDK, and that one T cell clone cross-reacted with the peptide derived from exogenous Ags such as E. coli PDC-E2, which has an EXDK sequence.
This is not only a definite demonstration of the T cell autoepitope of mitochondrial Ags in PBC, but also a demonstration of "molecular mimicry" that is operative at the T cell clonal level in human autoimmune diseases. The possible mechanism of molecular mimicry at the T cell clonal level is also discussed.

Materials and Methods
Patients. 13  Preparation of Synthetic Peptides Corresponding to PDC-E2. 40 different peptides composed of 13-20 amino acid residues corresponding to the amino acid sequence of human PDC-E2 were synthesized via F-moc chemistry using a peptide synthesizer (model 432A Synergy; Applied Biosystems Inc., Foster City, CA) (9,37). The peptides were purified by reverse-phase HPLC, and the purity of all peptides used in this study was >95 %, as determined by HPLC analysis. The peptides were designed according to the analysis of the amphipathic regions of the antigenic molecules and the presence of consensus motifs based on the studies of Berzofsky et al. (38). Synthetic peptides (SPs) used in this study, indicated by the amino acid number from the NH2 terminus of PDC-E2, were classified into seven groups as follows: group 1: SPs -40--21, -31 T Celt Proliferation Assay. PBMCs were separated from the peripheral blood by Ficoll-Isopaque gradient centrifugation. T cells were purified by rosetting PBMCs with sheep red blood cells. 1 x 10 s T cells and 1 x 104 autologous irradiated (3,000 rad) non-T cells per well were cultured in the presence of peptide mixtures (groups 1-7; each synthetic peptide concentration was 10 #g/ml) in a 96-well round bottom plate (Costar Corp., Cambridge, MA) in RPMI 1640 supplemented with 2 mM t-glutamine, 50 ng/ml of gentamycin, and 10% human AB-positive serum (complete RPMI medium) at 37~ in a humidified 5% CO2 atmosphere. In each experiment, microcultures containing T cells and irradiated non-T cells, but no Ag served as negative controls. More than 30 wells were studied in each group. After 7 d of culture, the T cells were restimulated with the same concentration of Ag or without Ag in the presence of 5 x 10 g freshly prepared, irradiated (3,

Establishment of Ag-specific T Cell Clones. The microcultures
showing positive proliferation were kept in culture in the presence of freshly prepared autologous antigen-presenting cells (APCs) in complete RPMI medium containing the same peptide mixture (each peptide concentration was 10 #g/ml) and 20 U/ml IL-2 (Takeda Medical Co., Tokyo, Japan). The cells were repeatedly stimulated with the same Ag in the presence of irradiated autologous PBMCs every week. After four to five repeated stimulations, these T cell lines were cloned at 0.5 cell per well in complete R.PMI medium containing IL-2 (100 U/ml) in the presence of autologous irradiated (3,000 tad) PBMCs as feeders. The peptide mixture-specific T cell clones were expanded and studied in the following experiments.

Analysis of the Cell Surface Phenotypes of T Cell Clones by Flow
Cytometry. T cell clones were stained with a variety of FITC-or PE-conjugated mAbs, including mAbs to CD3 (anti-Leu4), CD4 (anti-Leu32a), CD8 (anti-Leu2a), CD45RA (2H4), CD45R.O (UCHL-1), and TCR. All of these mAbs were purchased from Becton Dickinson Immunocytometry Systems (Mountain View, CA). T cell clones were first incubated with an adequate concentration of these FITC-or PE-conjugated mAbs at 4~ for 30 rain. After washing the cells with PBS containing 0.1% sodium azide (Sigma Chemical Co.), the cells were analyzed by flow cytometry (FACScan| Becton Dickinson). kindly provided by Dr. T. Sasazuki, Division of Genetics, Medical Institute ofBioregulation, Kyushu University, Kyushu, Japan). 5 x 104 T cells were seeded in a 96-well, round-bottom plate containing 5 x 104 irradiated (3,000 rad) autologous PBMCs and synthetic peptide in the presence or absence of various mAbs. All mAbs were used at a 1:100 dilution of ascites. After 3 d of culture, a T cell proliferation assay was similarly performed in triplicate as previously described.

Determination of the Critical Amino Acids of T Cell Epitopes for the Recognition by TCR or for the Binding to HLA DR Using Alanineor Serine-substituted Peptides of SP 163-176.
To determine the amino acids of SP 163-176 critical for the recognition by TCR (epitope) or for the binding to HLA (anchor), five T cell clones specific for SP 163-176 were studied for their proliferative response to alanineor serine-substituted peptides of SP 163-176. In some experiments, alanine-or serine-substituted peptides were used as competitors for the original peptide 163-176 in a T cell proliferation assay.
PCR-based DNA Typing of HLA Class II Genes. The DNA typing of HLA class II genes was performed using a PCR/sequencespecific oligonucleotide probe (SSOP) analysis in 13 PBC patients and 7 healthy subjects as described elsewhere (39). Genomic DNA was extracted from peripheral granulocytes and subjected to PCR. in 10 mM Tris-HC1 (pH 8.4 at 24~ 50 mM KC1, 2.0 mM MgClz, 0.1 mg/ml gelatin, 0.02% NP-40 to amplify the second exons of the DR.B1, DQA1, DQB1, DPA1, or DPB1 genes, using thermostable DNA polymerase. Amplified DNA was spotted onto a nylon membrane (Hybond N +; Amersham International), and it was immobilized by alkaline denaturation in 0.4 N NaOH. The hybridization procedure with 140 types of SSOPs has been described previously (39). 11 positive hybridization signals were obtained by exposing the filters to x-ray film (XAR-5; Eastman Kodak Co., Rochester, NY) at room temperature for 30 min.

Results
Proliferative Response of T Cells to Synthetic Peptides Corresponding to Human PDC-E2. We studied the T cell prolifer-alive response to synthetic peptides corresponding to putative T cell epitopes of human PDC-E2 (Fig. 1). The T cells derived from the majority of patients with PBC proliferated in response to synthetic peptide groups 2, 3, and 6 (the mean values __ SD of stimulation indices ranged from 1.9 +_ 0.4 to 2.6 _ 0.9), but not to groups 1, 4, 5, and 7 (the mean values +__ SD of stimulation indices ranged from 1.0 _+ 0.2 to 1.4 _ 0.4).

Generation and Characterization of T Cell Clones Specific for Peptides Corresponding to Human PDC-E2. Microcultures that
were stimulated by peptide mixture group 2, 3, or 6 and showed a value of [3H]TdR incorporation two times higher than the mean value of microcultures without any peptides were repeatedly stimulated with the same group of peptide mixtures (group 2, 3, or 6) in the presence of irradiated autologous PBMCs and IL-2 (20 U/ml) once every week. After four to five repeated stimulations, the T cell lines were cloned at 0.5 cell per well. Consequently, six T cell clones that proliferated in response to peptide mixture group 3 were obtained from four different patients (Table 1). These T cell clones responded to SP 163-182, but not to other peptides contained in the group 3 peptide mixture (Fig. 2). Whereas all T cell clones proliferated in a dose-dependent manner in response to SP 163-182 (Fig. 3), they did not proliferate in response to other Ags, such as OVA or OGDC. Furthermore, the proliferation of these peptide-specific T cell clones was inhibited by mAbs such as anti-CD3, anti-CD4, and anti-HLA DR (Fig. 3). The surface phenotypes of these T cell clones were CD3 +, CD4 +, CD45RO +, and TCRot~ +, as determined by a flow cytometric analysis (Table 1).

HLA Restriction ofT Cell Clones Specific for SP 163-182.
To identify the HLA molecules responsible for Ag presentation of SP 163-182 to T cell clones, we used allogeneic irradiated PBMCs with various HLA haplotypes as APCs. Briefly, the irradiated allogeneic PBMCs (5 x 104 per well) and each       The other two T cell clones, T-pep-2-2 and T-pep-11-1, did not proliferate in response to these two peptides with EXDK sequences. None of the T cell clones proliferated in response to human glycogen phosphorylase/~ 354-367 or HLA D R c~ chain 82-95.

Discussion
Although mitochondrial Ags are present in the inner membranes of mitochondria in every cell type in the body, the autoimmune process in PBC is restricted to the liver; the infiltration of T cells, B cells, and macrophages is distributed mainly around the biliary ductular tissues in the liver (2,(10)(11)(12). This organ-specific autoimmune process in PBC, though non-organ-specific target self Ags are present, may be explained by the specific expression of mitochondrial Ags in addition to HLA DR. and DQ molecules on or near the luminal surface of biliary epithelial cells in the liver (13)(14)(15)(16)(17). B and T cells infiltrating the liver produce AMAs and proliferate in response to PDC or OGDC in vitro, respectively (14,(18)(19)(20). E2, Elc~, and EI~ components and protein X of PDC and E2 components of OGDC and BCOADC have also been identified as autoantigens recognized by AMAs (3)(4)(5)(6)(7)(8)(9).
Based on these observations, it is very likely that the immune response to mitochondrial Ags, such as PDC, OGDC, and BCOADC in the liver, plays a central role in the pathogenesis of PBC. Therefore, the identification of the immunodominant autoepitopes and HLA molecules involved in the immune response to mitochondrial Ags could possibly clarify the pathogenesis of PBC and establish therapeutic strategies to prevent the occurrence or the progression of PBC. However, thus far, there have been no reports on the T cell autoepitopes of mitochondrial Ags at the molecular level or their MHC restriction molecules (14,(18)(19)(20). We previously found that PDC-specific T cells are circulating in the peripheral blood of patients with PBC, and that all T cell lines specific for PDC proliferate in response to PDC-E2, indicating that PDC-E2 contains the immunodominant T cell autoepitopes of PDC (data not shown). Therefore, in the present study, we tried to generate PDC-E2-specific T cell clones by using various peptides covering PDC-E2 as selecting Ags. The characterization of six PDC-E2-specific T cell clones successfully generated in the present study showed the following: (a) minimal T cell autoepitopes of T cell clones specific for PDC-E2 were all located on the same region of PDC-E2 peptide 163-176 (GDLLAEIETD-KATI), which corresponds to the inner lipoyl domain of human PDC-E2; (b) all T cell clones specific for human PDC-E2 163-176 are restricted by the same MHC molecule, HLA DRB4 0101; (c) E, D, and K at positions 170, 172, and 173 are common essential amino acid residues for this T cell epitope; (d) all T cell clones specific for human PDC-E2 163-176 react to PDC-E2 peptide [36][37][38][39][40][41][42][43][44][45][46][47][48][49], which corresponds to the outer lipoyl domain of human PDC-E2; (e) one T cell clone (T-pep-11-2) cross-reacts with exogenous Ags, such as E. coli PDC-E2 peptide 31-44/134-147/235-248 (EQSLITVEGDKASM), which has EXDK sequences, but none of the T cell clones cross-react with P. putida BCOADC peptide 104-117 (DELLATIETDKIDI), which has EXDK sequences; and (f) none of the T cell clones crossreact with self-peptides derived from human glycogen phosphorylase B or HLA DR ot chain, which share amino acid homology with human PDC-E2 163-176 but do not have EXDK sequences.
It has been hypothesized that PBC may have a bacterial etiology because of the high incidence of recurrent urinary tract infection in patients with PBC (1,2,8). Furthermore, the sera from patients with PBC react with both human PDC-E2 and E. coli PDC-E2 (8,9). This is because PDC-E2 peptides are evolutionarily highly conserved among different species, especially in their lipoic acid-binding sites (4)(5)(6). Thus, a mechanism of molecular mimicry has been proposed as a possible cause of PBC (40). In this hypothesis, the T cells first recognize the lipoyl domain orE. coli PDC-E2 containing 1841 Shimoda et al.
EGDKA sequences. Then, these T ceils cross-react with self peptides containing AVDKA sequences from HLA DR c~ chain or ETDKA sequences from human PDC-E2 by abetrandy expressed class II HLA molecules on biliary epithelial cells (13)(14)(15)(16)(17). Finally, this initiates the autoimmune cascade leading to the destruction of the bile ducts in which AMAs and/or autoreactive T cells specific for mitochondrial Ags may play a pathogenic role. At this stage, the autoimmune process takes place in the absence of the exogenous Ags, such as E. coli PDC-E2, which initiated the immune response. In some animal models of autoimmune diseases, such as experimental allergic encephalomyelitis and autoimmune oophoritis, the mechanism of molecular mimicry has been proven to be operative in vivo (41)(42)(43)(44)(45)(46)(47).
In this study, we demonstrated the presence of a T cell clone specific for human PDC-E2 163-176 (GDLLAEIETD-KATI) that cross-reacts with the lipoic acid-binding site of E. coli PDC-E2 (EQSLITVEGDKASM). This is the proof that molecular mimicry between human and E. coli PDC-E2 can be operative at the T cell donal level in PBC. On the other hand, none of T cell clones specific for PDC-E2 crossreacted with HLA DR c~ chain peptide 82-95 (QGALAN-IAVDKANL) or human glycogen phosphorylase 3 peptide 354-367 (LVDLERMDWDKAWD), which share amino acid homology with PDC-E2 but have no EXDK sequences. This finding indicates that the presence of amino acid homology per se is not sufficient to provoke the cascade of molecular mimicry. Moreover, it is important that clone T-pep-11-2 crossreacted with E. coli PDC-E2 (EQSLITVEGDKASM), but not with P. putida PDC-E2 (DELLATIETDKIDI), which not only has EXDK sequences, but also has greater amino acid homology with human PDC-E2 163-176 than E. coli PDC-E2(EQSLITVEGDKASM). To explain this phenomenon of cross-reactivity at the T cell donal level, it will be necessary to dissect the molecular mechanism of the MHC class II-peptide-TCK interaction.
The recognition of peptide fragments in the context of class II MHC molecules by T cells is a central event in the development of the immune response (48)(49)(50). Proteolytic fragments of peptides processed by APCs that match the physiochemical character of the peptide-binding grooves formed by ot and 3 chains of class II MHC molecules are expressed on the surface of APCs and are recognized by T cells (48)(49)(50). The structural motifs of peptides capable of binding to HLA DR have been determined based on the peptide sequences eluted from purified DR complexes (51,52) or phage peptide libraries (53,54). These reports indicated that only certain residues are involved in allele-specific peptide binding, whereas the other residues are promiscuous (51)(52)(53)(54). An analysis of the crystal structure ofHLA DRB1 0101 protein complexed with an influenza virus peptide demonstrated the exact structural explanation for the MHC class II-peptide-TCR interaction at the molecular level (50). Because polymorphic residues of DR alleles are scattered within the peptide-binding grooves, different DR molecules are capable of binding peptides with different structural motifs, and this phenomenon contributes to the HLA-linked polymorphism of the immune response: DRB1 0405 confers increased susceptibility to rheumatoid arthritis, but not to insulin autoimmune syndrome, whereas DRB1 0406 conversely confers susceptibility to the latter but not to the former.
To date, motifs for binding peptides have been reported in various DR molecules, including DR1 (DRB1 0101), DR2 (DRB1 1501), DR3 (DRB1 0301), DR4 (DRB1 0401, DRB1 0405, DRB1 0406), DR11 (DRB1 1101), DR7 (DRB1 0701), and DR8 (DRB1 0801) (24,(52)(53)(54)(55), indicating that two or three hydrophobic amino acids are necessary for the binding of the peptide to HLA hydrophobic pockets. However, no peptide-binding motif of HLA DRB4 0101 has been reported. Although the precise analysis of the peptide-binding motif of HLA DRB4 0101 is now underway using HLA DRB4 0101-transfected L cells and various modified peptides based on PDC-E2 peptide 163-176 (GDLLAEIETDKATI), our preliminary study indicates that LXXIXXD is an HLA DRB4 0101-binding motif. If this is the case, the E and K at positions 170 and 173 may be crucial TCR-binding sites, and the amino acid at position 169 (I for human and P. ioutida PDC-E2 and V for E. coli PDC-E2) may have an important effect on the structure of the TCR-binding site. The rationale for the development of molecular mimicry at the T cell clonal level is now under investigation using T cell clones specific for human PDC-E2 163-176 (GDLLAEIETDKATI) and/or E. coli PDC-E2 (EQSLITVEGDKASM) and various peptides that share amino acid homology with these peptides.
In Caucasians, PBC has been reported to be associated with HLA DR3 (56), HLA DRw8 (57), and possibly HLA DR4 (58). An association with HLA DR2 (59) and DP B1 0501 (60) has been reported in Japanese patients with PBC. In other studies, no such associations were found with HLA Ags (61). Thus, no consensus seems to exist concerning the associa-tions between PBC and HLA. In the present study, all T cell clones from four different patients with PBC recognized human PDC-E2 163-176 in the context of the same HLA allele, HLA DRB4 0101, indicating that PDC-E2 peptide 163-176 plays a central role in at least all patients with PBC who have the HLA DRB4 0101 allele. The ratio of HLA DRB4 0101 positivity among patients with PBC is ~77%. This is similar to the control Japanese population (62), indicating that the possession of HLA DRB4 0101 may not be a genetic predisposition for PBC. However, in contrast to the highest degree of polymorphism of HLA DRB1, polymorphism ofHLA DRB4 0101 has not been reported. Therefore, it is possible that the HLA DRB4 0101-binding PDC-E2 peptide identified in the present study could provide important information for the development of peptide-specific immunotherapy in the majority of patients with PBC who have an HLA DRB4 0101 allele.
Interestingly, the T cell epitope of PDC-E2 peptide 163-176 almost completely overlaps with the B cell epitopes that were identified in the inner lipoyl domain of PDC-E2 (PDC-E2 165-184 with lipoic acid located at K at 174) (7)(8)(9). In addition, all T cell clones specific for PDC-E2 peptide 163-176 cross-reacted with PDC-E2 peptide 36-49, which corresponds to the outer lipoyl domain of PDC-E2. This PDC-E2 outer lipoyl domain was also shown to be the immunodominant B cell epitope of PDC-E2 that cross-reacts with the B cell epitope of the inner lipoyl domain of PDC-E2 (7-9). Recently, "universal" T cell epitopes of certain viruses have been found to be located near the B cell epitopes, indicating that the regions containing both T and B cell epitopes can be highly immunogenic (37,(63)(64)(65)(66). Although there have been no reports theoretically showing the exact relationship between T and B cell epitopes of self Ags, our results may indicate the possibility that peptides of self Ags containing both T and B cell epitopes can be highly immunogenic autoepitopes that cause various autoimmune responses. In this aspect, we speculate that the region corresponding to or overlapping PDC-E2 peptide 163-176 can also be a T cell autoepitope in the context of MHC class II molecules other than the HLA DRB4 0101 allele. We are now trying to identify the T cell autoepitopes in patients with PBC who have no HLA DRB4 0101 allele.
In conclusion, the present study not only is a definite demonstration of an immunodominant T cell autoepitope of PDC-E2, but it is also a demonstration of the molecular mimicry that is operative at the T cell clonal level in PBC. Based on these findings, it is considered possible to develop a strategy for the peptide-specific immunotherapy in PBC.
We thank Dr. S. Matsushita