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1From the Department of Ophthalmology and Visual Science, Tokyo Medical and Dental University Graduate School of Medicine, Tokyo, Japan; the 2Departments of Ophthalmology and 3Immunology, Kurume University School of Medicine, Fukuoka, Japan.
| Abstract |
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METHODS. T-cell clones (TCCs) were established from cells infiltrating the aqueous humor and from peripheral blood mononuclear cells (PBMCs) of patients with VKH. The target cells were LDR4-transfected cells (HLA-DRB1*0405). The TCCs were cocultured with LDR4 in the presence of tyrosinase (tyrosinase450-462: SYLQDSDPDSFQD), gp100 (gp10044-59: WNRQLYPEWTEAQRLD), or a control peptide. The immune response was evaluated by cytokine production. The responding melanocyte peptide-specific VKH-TCCs were characterized by an immunofluorescence method with flow cytometry. A search was made for molecular mimicry among tyrosinase450-462, gp10044-59, and exogenous antigens, such as viruses, by database screening.
RESULTS. Cells infiltrating the eye and PBMCs in HLA-DR4+ (HLA-DRB1*0405, 0410) patients with VKH contained a population of CD4+ T lymphocytes that recognized tyrosinase and gp100 peptides and produced RANTES and IFN-
in response to the two peptides. The T cells were active memory Th1-type lymphocytes, and they recognized the tyrosinase peptide and produced IFN-
in response to HLA-DRB1*0405+ melanoma cells. Cytomegalovirus envelope glycoprotein H (CMV-egH290-302) had high amino acid homology with the tyrosinase peptide. In addition, some of the VKH-TCCs recognized CMV-egH290-302 peptide, as well as the tyrosinase peptides.
CONCLUSIONS. In VKH there are tyrosinase and gp100 peptide-specific T cells that can mediate an inflammatory response. Such melanocyte antigen-specific T cells could be associated with the cause and pathology of VKH disease.
Although the disease appears to be caused by autoimmune responses to melanocytes or melanocyte-associated antigens, it is still not known what antigens or antigen peptides among the melanocyte-associated antigens are responsible for the disease. It has been shown that several melanoma peptides are recognized by cytotoxic T lymphocytes (CTLs), and MART-1,7 gp100 (Pmel-17),8 gp75,9 tyrosinase,10 11 and melanocyte lineage-specific peptides are expressed not only on melanoma cells but also on human melanocytes. Many epitopes of these peptides are recognized by HLA-class I-restricted CTLs. For example, in our previous study, the CTLs from the eyes of patients with VKH recognized MART-1 peptide in an HLA-A2-restricted manner.12 However, VKH disease is known to be highly associated with HLA-DR4 (HLA-DRB1*0405). Therefore, the candidate peptides responsible for the immunopathogenic mechanism of the disease should be recognized by T cells in an HLA-DR4-restricted manner.
Tyrosinase and gp100 are melanoma-associated antigen peptides that have been shown to be recognized by CD4+ T cells in an HLA-DR4-restricted manner.13 14 The purpose of this study was to determine whether these melanocyte-associated peptides are responsible for the immunopathogenic mechanisms of VKH disease. In addition, we examined whether a viral infection could be a trigger mechanism. We first identified the melanocyte antigen peptides that could play a role in the development of the disease, and then used database screening to search for homology between the melanocyte peptides and antigen peptides of exogenous pathogens.
| Materials and Methods |
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Antigen Peptides
Two HLA-DRB1*0405 human binding melanocyte peptides were used: a 13-mer peptide (tyrosinase450-462: SYLQDSDPDSFQD) and a 16-mer peptide (gp10044-59: WNRQLYPEWTEAQRLD). The major histocompatibility complex (MHC) class II binding motif of these two peptides was HLA-DRB1*0405 binding peptide.15 An influenza peptide HA307-319 (PKYVKQNTLKLAT) was used as the negative control. These peptides are known to bind to HLA-DRB1*0401 with high affinity.16 Some analogues of tyrosinase450-462 were also used. We selected these analogues of tyrosinase450-462 from the report of Topalian et al.13 All peptides were synthesized by BioSynthesis Inc. (Lewisville, TX), and the purity of the peptides was >95%, as determined by HPLC analysis.
mRNA Expression of Melanocyte Antigens on Ocular Tissues
To confirm that tyrosinase and gp100 were present in human ocular tissues, especially in patients with VKH, the expression of the mRNA of tyrosinase and gp100 in human iris was determined by RT-PCR. The samples of iris and trabecular meshwork were obtained from a patient with VKH disease during glaucoma surgery. A melanoma cell line, MMAc, was used as the positive control. Total cellular RNA was extracted from the tissues (TRIzol Reagent; Invitrogen, Gaithersburg, MD), and the melanoma cell line was prepared. Reverse transcription was performed (SuperScriptTM II; Invitrogen). The cDNA obtained was tested for the presence of defined gene sequences by PCR (Ex-Taq kit; Takara Shuzo Co., Ltd., Shiga, Japan) on 25 µL using specific primer pairs. The following primers were used for the PCR reaction: ß-actin sense, 5'-CTT CGC GGG CGA CGA TGA-3', and anti-sense, 5'-CGT ACA TGG CTG GGG TGT TG-3', yielding an amplification product of 340-bp; tyrosinase sense, 5'-AAG AAA TCC AGA AGC TGA CAG GAG ATG-3' and anti-sense, 5'-TGC TTT GAG AGG CAT CCG CTA TC-3', amplifying a 423-bp fragment; gp100 sense, 5'-CTG TGC CAG CCT GTC TAC-3', and anti-sense, 5'-CAC CAA TGG GAC AAG AGC AG-3', amplifying a 334-bp fragment. Amplification of tyrosinase, gp100, and ß-actin as positive control transcripts required 40 cycles, including a 30-second annealing step at 55°C and a 30-second extension at 72°C.
The RT-PCR products were run on 1.5% agarose gels in the presence of ethidium bromide, and the gels were then photographed under ultraviolet transillumination.
TCCs and T-Cell Lines
An aliquot of AH was obtained from patients with different types of uveitis whose eyes were inflamed. PBMCs were obtained from the patients before and during systemic corticosteroid therapy. TCCs were established from these samples by the limited-dilution method.12 17 18 There were 16 TCCs from the AH of four patients with VKH (P25, Table 1 , Fig. 4 ) and 2 TCCs from the PBMCs of a patient (P1) with VKH disease. The TCCs established from other types of uveitis were used: three clones from the AH and four clones from the vitreous fluid of three patients with Behçets disease, and four clones from the AH of a patient with sarcoidosis. The TCCs established from PBMCs of healthy donors (HD1 and -2 in Table 1 ) were also used. The cloning efficiency was approximately 15% to 50%.
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4 weeks. The experiments were performed at least twice with similar results.
Assays for Cytokine Production and Phenotype of TCC
Cell-free supernatants were obtained from each TCC by centrifuging and collecting the supernatant. An ELISA kit (R&D Systems, Minneapolis, MN) was used to detect and quantify the cytokines and chemokines. The ability of T cells to produce cytokines and chemokines was determined by using the TCCs of patients with VKH. The cytokines and chemokines measured were IL-1
, IL-2, IL-4, IL-6, IL-10, TNF-
, IFN-
, GM-CSF, IL-8 (CXC chemokine ligand 8, CXCL-8), MIP-1
(CC chemokine ligand 3, CCL-3) and -ß (CCL-4), and RANTES (CCL-5).
The phenotype of a TCC was determined by the double-color immunofluorescence technique with flow cytometry. T cells were washed with PBS and were incubated at 4°C for 30 minutes with the following antibodies: FITC-conjugated mAb NU-Ts/c (CD8; Nichirei, Tokyo, Japan); anti-HLA-DR (BD Biosciences, Mountain View, CA); CD45RA (BD PharMingen, SanDiego, CA); CXCR3 (Genzyme, Cambridge, MA); TCR-
/ß (BD PharMingen); a PE-conjugated mAb, NU-Th/i (CD4; Nichirei); CD45RO (BD PharMingen); CXCR1 (Genzyme); and TCR-
/
(BD PharMingen). Anti-Tac mAb (CD25) was used as the primary reagent, with FITC-conjugated goat IgG against mouse IgG (Tago, Inc., Burlingame, CA) used as the secondary reagent. The biotinylated NOK-1 (CD95 ligand) was used as the primary reagent and FITC-conjugated avidin (BD PharMingen) was the secondary reagent.
Database Screening to Melanocyte Antigens
Database screening (GenBank database screening) was performed to determine whether tyrosinase450-462 and gp10044-59 had homologous amino acid sequences to exogenous antigens. The human cytomegalovirus envelope glycoprotein H peptide (CMV-egH290-302) was found to have a high amino acid homology to tyrosinase450-462 peptide (Table 4) . The MHC class II binding motif of the CMV-egH290-302 was also DRB1*0405.15
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In the screening assay, the peptides were used at a concentration of 50 µM because titration of the CD4+ T cell response to the peptides showed that a peptide concentration of more than 50 µM was needed to evoke significant reactivity.13 After the incubation, cell-free culture supernatants were harvested and used to measure RANTES or IFN-
. To determine the specificity of the response, the APCs (MMAc) were pretreated with mAbs that included anti-HLA-DR (IgG2b); anti-HLA-A, B, and C (IgG1); and anti-CD4 (IgG1; all BD PharMingen). As an isotype control, purified mouse IgG2a,
(BD PharMingen) was added to the appropriate cultures. To examine whether the T cells respond to CMV antigens, the TCCs from patients with VKH disease were cocultured with LDR4 cells in the presence of CMV-egH290-302. The specific response was evaluated by RANTES production assay.
Statistical Evaluation of Results
Each experiment was repeated at least twice with similar results. All statistical analyses were conducted with Students t-test. Differences were considered statistically significant at P < 0.05.
| Results |
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Detection of Tyrosinase and gp100 Gene Transcriptions in Human Iris
To determine whether tyrosinase and gp100 are present in ocular tissues, the expression of their genes was determined by RT-PCR using ocular tissues of a patient with VKH disease (Fig. 1) . A strong expression of the mRNA of tyrosinase was detected in iris tissues but not in trabecular meshwork tissues (Fig. 1A) . The expression of the mRNA of gp100 was also detected in iris tissues and in melanoma cell lines as the positive control (Fig. 1B) . ß-Actin was detected in all samples (data not shown).
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, 37; IFN-
, 64; GM-CSF, 24; MIP-1
/CCL-3, 370; MIP-1ß/CCL-4, 278; and RANTES/CCL-5, 581. In preliminary study using these cytokines and chemokines, the VKH TCCs indicated large response for IFN-
and RANTES in the presence of human melanocyte antigens, but not IL-6, IL-8, GM-CSF, and TNF-
. The RANTES and IFN-
production assays were used in the following experiments because they were produced in high amounts by the ocular-infiltrating T cells compared with the T cells from the PBMCs of patients with VKH and the ocular fluid from other types of uveitis. The lymphocytic responses to the HLA-DRB1*0405-restricted, melanocyte-associated peptides tyrosinase450-462 and gp10044-59 were tested by the RANTES-production assay (Table 1) . One CD4+ TCC (VKH1-2) established from the PBMCs of patient 1, one CD4+TCC (VKH2-1) from the AH of patient 2 and two CD4+TCCs (VKH3-1 and -4) from the AH of patient 3 responded more strongly to tyrosinase450-462 than to HA307-319, a control peptide. One CD4+TCC (VKH3-3) from the AH of patient 3 and two CD4+ TCCs (VKH4-1 and -2) from the AH2 of patient 4 responded more strongly to gp10044-59 than to HA307-319. In contrast, the TCCs from HLA-DR4+ patients with Behçets disease and sarcoidosis did not respond to tyrosinase450-462 or to gp10044-59 (Table 1) . The TCCs from PBMCs of HLA-DR4+ healthy donors also did not respond to all peptides (Table 1) .
All TCLs (TCL1-6) from the PBMCs of six patients with VKH (P4-9) responded more strongly to tyrosinase450-462 and gp10044-59 peptides than to HA307-319. In contrast, the TCLs from a patient with Behçets disease and with sarcoidosis did not respond to the two peptides (Table 2) . The TCLs from eight healthy donors who had no history of uveitis and were aged-matched to the patients with VKH did not respond to the two peptides (Table 2) . In addition, all TCLs from patients with VKH produced IFN-
in the presence of these melanocyte peptides much greater than control TCLs (Table 3) .
A dose-response study was performed to confirm that the T-cell response to tyrosinase450-462 peptide and gp10044-59 peptide was significant. The production of RANTES by VKH3-1 CD4+ TCC from the AH of a patient with VKH disease was upregulated by tyrosinase450-462 stimulation in a dose-dependent manner (Fig. 2A) . Similarly, the VKH4-1 CD4+ TCC responded strongly and in a dose-dependent manner to gp10044-59 (Fig. 2B) . A change of one amino acid at the anchor position of tyrosinase450-462 abolished the RANTES production by the TCL (TCL-2) in response to the peptide (Fig. 2C) . In addition, the production of IFN-
by VKH3-1 or VKH4-1 CD4+ TCCs was upregulated by the melanocyte-peptide stimulation in a dose-dependent manner (Fig. 2D) .
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/ß+ cells (Fig. 3A) . The cells were negative for CD8, CD45RA, CD95L, CXCR1, and TCR-
/
. Other TCCs (VKH2-1, VKH3-4, VKH3-10, and VKH5-2) established from ocular-infiltrating cells in patients with VKH indicated similar phenotypes (data not shown).
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in response to MMAc (Fig. 3B) , and IFN-
production was significantly reduced by anti-DR mAb and anti-CD4 mAb, but not by anti-class I mAb (Fig. 3B) or isotype control. Similarly, the VKH2-1 TCC produced a significant amount of IFN-
in response to MMAc, and the production was significantly reduced by anti-DR mAbs (data not shown). These results indicate that VKH3-1 TCCs are the Th1-type T cells that recognize melanocyte antigens in an HLA-DRB1*0405-restricted manner and produce significant amounts of IFN-
.
Lymphocytic Response of Patients with VKH to CMV Antigen and Melanocyte Antigen
Because tyrosinase450-462 is highly homologous to CMV-egH290-302 (Table 4) , we also examined its lymphocytic response to CMV-egH290-302. Six CD4+ TCCs established from the AH of patients with VKH responded significantly to CMV-egH290-302 (Fig. 4) . Some of the CD4+ T cells also responded significantly to tyrosinase450-462 but not to the peptide of control AH. Thus, TCCs established from patients with VKH without antigen stimulation contain CMV-egH290-302 peptidespecific T cells.
| Discussion |
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Tyrosinase is a type I transmembrane protein consisting of 529 amino acids and regulates melanin production,20 whereas gp100 is a membrane glycoprotein consisting of 661 amino acids and is present in melanosomes where melanin is synthesized.21 Tyrosinase and gp100 are expressed on both melanoma and melanocytes. Kawakami and Rosenberg22 reported that in patients with malignant melanoma who had immunotherapy against melanoma-specific antigens including tyrosinase and gp100 antigens, vitiligo developed as an adverse side effect of the therapy. They also demonstrated that IgG specific for melanoma protein preferentially expressed on melanoma and melanocytes was detected in the sera of 7 of 11 patients with VKH disease and some patients with melanoma.23 These tumor antigens were isolated from a patient with vitiligo. These observations suggest that the recognition of the melanoma-differentiation antigen can be associated with autoimmune depigmentation, vitiligo, which is one of the characteristic clinical symptoms of VKH disease. Therefore, it was hypothesized that the melanoma and melanocyte-specific antigens which recognized infiltrating T cells could be potential candidates for self-antigens of autoimmune disease against melanocytes.
Our previous results have demonstrated that MART-1-specific cytotoxic T cells isolated from the eye of patients with VKH disease lysed melanocytes in an HLA-A2-restricted manner.12 However, MART-1 is not an appropriate candidate for the pathogenic antigen of VKH disease because VKH is known to be associated with HLA-DR4 and not with HLA-A2. The pathogenic antigen should be HLA-DR4-restricted or an HLA-DRB*0405-restricted antigen.
Earlier, Yamaki et al.24 25 showed that the PBMCs of patients with VKH disease exhibited low but significant proliferation to tyrosinase peptides, and immunization of experimental animals with tyrosinase induced ocular inflammation. Recently, Damico et al.26 also reported that T cells established from PBMCs of patients with VKH responded to some peptides of tyrosinase, TRP-1, TRP-2, and Pmel-17 (gp100). Therefore, we focused on the role of ocular-infiltrating lymphocytes in VKH disease. For this purpose, we used TCCs established from cells infiltrating the eye of patients with VKH by the limited-dilution method.12 17 18 Our results showed that the TCCs obtained from the eyes of patients with VKH intrinsically produced large amounts of IFN-
, and RANTES. RANTES has a strong chemotactic effect on neutrophils and T lymphocytes and are produced by a variety of cells including T lymphocytes, particularly helper memory T cells.27 IFN-
is a major Th1 cytokine and has been reported to be involved in the pathogenesis of VKH disease.28 It is assumed that these cytokines can best represent the recognition of T cells in the reappearance of antigens. Our results showed that the production of RANTES by the TCCs obtained from patients with VKH was significantly upregulated when cultured with tyrosinase450-462 or gp10044-59, but not with control peptides. The TCCs obtained from eyes with other uveitic diseases, such as Behçets disease and sarcoidosis, did not respond significantly to the two peptides, indicating that the lymphocytic response to the peptides was disease specific.
The lymphocytic response was blocked by anti-DR and anti-CD4 antibodies indicating that the response was MHC class IIrestricted. The phenotype of the TCCs was active memory Th1 cells. The TCLs established from the PBMCs of patients with VKH disease, but not those with Behçets disease or sarcoidosis or healthy control subjects, also induced a significant increase of RANTES production in response to the two melanocyte-associated peptides. These results indicated that active memory T lymphocytes are present in the eye and the peripheral circulation of patients with VKH disease, and they play a significant role in recognizing the melanocyte-associated peptides to induce immunologic response to the peptides.
It is of interest to note that vitiligo develops in patients with malignant melanoma as an adverse side effect of immunotherapy targeting melanoma-associated antigens, including tyrosinase and gp100.22 This clinical observation suggests that the immunologic recognition of the melanoma-associated antigen can be associated with the autoimmune depigmentation vitiligo, which is one of the most characteristic clinical features of VKH disease.
An important finding in our study was that the CD4+ T lymphocytes, that recognize the tyrosinase peptide, responded significantly to an antigen that had homologous amino acids to tyrosinase peptide. This antigen was the common cytomegalovirus of humans. The clinical onset of VKH is characterized by a sudden appearance of bilateral ocular inflammation with prodromal symptoms such as a common cold. This suggests that some viral infection may act as a trigger mechanism. We are now conducting experiments on whether T cells established from ocular fluids or PBMCs of patients with VKH cross-react with tyrosinase450-462 and CMV-egH290-302; whether VKH-PBMCs under antigen stimulation respond to the antigens; whether seropositivity to CMV is higher in patients with VKH disease; and whether the CMV infection in patients with VKH is latent.
In conclusions, patients with VKH disease have immune responses specific to the melanocyte antigens, tyrosinase450-462 and gp10044-59. The melanocyte antigen-specific T cells could be associated with the cause and pathologic course of VKH disease. However, the mechanisms by which Th1 lymphocytes are sensitized by self-antigens, tyrosinase, and gp100 and cause the immune responses to the antigens are still unknown. We are now investigating whether melanocyte antigens from patients with VKH disease cross-react with exogenous antigens such as those of viruses.
| Acknowledgements |
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| Footnotes |
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Submitted for publication December 5, 2005; revised January 10 and 29, 2006; accepted March, 22, 2006.
Disclosure: S. Sugita, None; H. Takase, None; C. Taguchi, None; Y. Imai, None; K. Kamoi, None; T. Kawaguchi, None; Y. Sugamoto, None; Y. Futagami, None; K. Itoh, None; M. Mochizuki, None
The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked "advertisement" in accordance with 18 U.S.C.
1734 solely to indicate this fact.
Corresponding author: Sunao Sugita, Department of Ophthalmology and Visual Science, Tokyo Medical and Dental University Graduate School of Medicine, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan; sunaoph{at}tmd.ac.jp.
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