E.H. Kemp

The Transcription Factors SOX9 and SOX10 Are Vitiligo Autoantigens in Autoimmune Polyendocrine Syndrome Type I

Vitiligo is common in the hereditary disorder autoimmune polyendocrine syndrome type I (APS I). Patients with APS I are known to have high titer autoantibodies directed against various tissue-specific antigens. Using sera from APS I patients for immunoscreening of a cDNA library from human scalp, we identified the transcription factors SOX9 and SOX10 as novel autoantigens related to this syndrome. Immunoreactivity against SOX9 was found in 14 (15%) and against SOX10 in 20 (22%) of the 91 APS I sera studied. All patients reacting with SOX9 displayed reactivity against SOX10, suggesting shared epitopes. Among the 19 patients with vitiligo, 12 (63%) were positive for SOX10 (p < 0.0001). Furthermore, three of 93 sera from patients with vitiligo unrelated to APS I showed strong reactivity against SOX10, which may indicate a more general role of SOX10 as an autoantigen in vitiligo.

Autoimmunity as an aetiological factor in vitiligo.

Vitiligo is a common dermatological disorder characterized by the presence on the skin of depigmented macules resulting from the destruction of cutaneous melanocytes. Autoimmunity is an important hypothesis with regard to vitiligo aetiology and the evidence for autoimmune responses being involved in the pathogenesis of this disorder will be discussed in the present review. All immune system compartments, including innate and adaptive immunity have been implicated in vitiligo development. Particularly relevant are autoantibodies and autoreactive T cells in vitiligo patients that have cytotoxic effects upon pigment cells. Furthermore, predisposition to vitiligo appears to be associated with certain alleles of the major histocompatibility complex class II antigens as well as with other autoimmune‐susceptibility genes. Moreover, the association of vitiligo with autoimmune disorders, the animal models of the disease, and the positive response to immunosuppressive therapeutic agents emphasize the role of autoimmunity in the development of this disorder.

A single-nucleotide polymorphism in the gene encoding lymphoid protein tyrosine phosphatase ( PTPN22 ) confers susceptibility to generalised vitiligo

Vitiligo is an acquired hypomelanotic skin disorder resulting from the loss of functional melanocytes from the cutaneous epidermis and autoimmunity has been suggested to play a part in its pathogenesis. Recently, the missense R620W polymorphism in the PTPN22 gene, which encodes lymphoid protein tyrosine phosphatase (LYP), has been associated with susceptibility to autoimmune disorders. The objective of this study was to ascertain if the disease-associated 1858T allele was also associated with generalised (nonsegmental) vitiligo and so the frequencies of the PTPN22 1858C/T alleles were investigated in 165 English patients with generalised vitiligo and 304 ethnically matched control subjects. The results indicated that the 1858T allele was significantly over-represented in the vitiligo patient group compared with the control cohort. Of 330 vitiligo alleles, 48 (14.5%) encoded the Trp620 variant compared to 52 of 608 (8.6%) control alleles (P=0.006; odds ratio=1.82, 95% confidence interval=1.17–2.82). The results indicate that the LYP missense R620W polymorphism may have an influence on the development of generalised vitiligo and provide further evidence for autoimmunity as an aetiological factor with respect to this disease.

Function-blocking autoantibodies to the melanin-concentrating hormone receptor in vitiligo patients.

Vitiligo is a common depigmenting skin disorder resulting from the loss of melanocytes in the cutaneous epidermis. Although the cause of the disease remains obscure, autoimmune mechanisms are thought to be involved. Recently, melanin-concentrating hormone receptor (MCHR)-binding autoantibodies have been identified in vitiligo patients. In the present study, we aimed to determine if MCHR autoantibodies could also affect receptor function either by direct activation or by blocking its response to melanin-concentrating hormone. The results indicated that 10/18 (56%) vitiligo patient IgG samples inhibited the function of MCHR expressed in a Chinese hamster ovary cell line. In contrast, neither control (n=20) nor SLE patient (n=10) IgG samples blocked receptor function. Compared with healthy controls, MCHR function-blocking autoantibodies were found at a significantly increased frequency in the vitiligo patient group (P=0.0004). No MCHR-activating autoantibodies were detected in any of the vitiligo patient, SLE patient or control IgG samples that were analysed. In addition, vitiligo patient IgGs were tested for MCHR autoantibodies that could mediate antibody-dependent cell-mediated cytotoxicity via the receptor. However, this could only be demonstrated in two vitiligo patient sera. Overall, this work has provided additional evidence that MCHR is a B-cell autoantigen in vitiligo and has demonstrated the existence of MCHR function-blocking autoantibodies further to the receptor-binding autoantibodies previously reported.

Autoantibodies in vitiligo patients are not directed to the melanocyte differentiation antigen MelanA/MART1

Recent studies have demonstrated the presence of circulating MelanA (MART1)‐specific cytotoxic T lymphocytes in a significant number of vitiligo patients when compared to control subjects. High levels of the skin‐homing receptor cutaneous lymphocyte‐associated antigen were expressed on the T cells and their frequency correlated with the extent of depigmentation and disease activity in the vitiligo patients. The present study was designed to examine vitiligo patient sera for the presence of autoantibodies to MelanA. The incidence of autoantibodies to MelanA in patients with vitiligo (n = 51) and in healthy individuals (n = 20) was examined using a radiobinding assay with 35S]‐labelled MelanA and using Western blot analysis with a glutathione S‐transferase (GST)‐MelanA fusion protein. Autoantibodies to MelanA could not be detected in any of the vitiligo patient sera or control sera analysed using either of these detection systems. It is therefore possible that MelanA only induces cellular rather than humoral autoreactivity in vitiligo.

Molecular mapping of epitopes on melanocyte-specific protein Pmel17 which are recognized by autoantibodies in patients with vitiligo

Previously, we reported the identification of Pmel17 autoantibodies in some patients with vitiligo. Here, we have determined the B cell epitopes on Pmel17 which are recognized by these autoantibodies. Deletion derivatives of Pmel17 cDNA were constructed using either subcloning of specific cDNA fragments or polymerase chain reaction amplification. Full‐length Pmel17 cDNA and its truncated derivatives were then translated in vitro to produce [35S]‐labelled proteins. The radiolabelled ligands were used subsequently in radiobinding assays to investigate the reactivity of sera from vitiligo patients. Two epitope regions were identified: one located at the C‐terminal end of Pmel17 between amino acids 634–644 and one in a central region of the protein between amino acids 326–341. Computer analysis of the potential B cell epitopes on Pmel17 revealed that the epitope domain encompassing amino acids 326–341 was located in an area of the protein which was predicted to be highly antigenic. In contrast, the epitope identified at the C‐terminal of Pmel17 (amino acids 634–644) was located in a region of the protein predicted to have low antigenicity. The amino acid sequences of the identified Pmel17 epitopes were compared to the amino acid sequences of the related melanogenic enzymes tyrosinase, tyrosinase‐related protein‐1 and tyrosinase‐related protein‐2. However, no sequence homology was found between either of the Pmel17 epitopes and the aforementioned proteins. This finding is consistent with our previous study in which we were unable to show the presence of Pmel17 antibodies which were cross‐reactive with either tyrosinase, tyrosinase‐related protein‐1 or tyrosinase‐related protein‐2. It also suggests that the IgG response to Pmel17 is distinct from the antibody response to the other melanocyte‐specific antigens.

Is there loss or qualitative changes in the expression of thyroid peroxidase protein in thyroid epithelial cancer

There is disagreement concerning the expression of thyroid peroxidase (TPO) in thyroid cancer, some studies finding qualitative as well as quantitative differences compared to normal tissue. To investigate TPO protein expression and its antigenic properties, TPO was captured from a solubilizate of thyroid microsomes by a panel of murine anti-TPO monoclonal antibodies and detected with a panel of anti-human TPO IgGκ Fab. TPO protein expression in 30 samples of malignant thyroid tissue was compared with TPO from adjacent normal tissues. Virtual absence of TPO expression was observed in 8 cases. In the remaining 22 malignant thyroid tumours the TPO protein level varied considerably from normal to nearly absent when compared to normal thyroid tissue or tissues from patients with Graves’ disease (range less than 0.5 to more than 12.5 μg mg–1 of protein). When expressed TPO displayed similar epitopes, to that of TPO from Graves’ disease tissue. The results obtained by the TPO capturing method were confirmed by SDS-PAGE and Western blot analysis with both microsomes and their solubilizates. The present results show that in about two-thirds of differentiated thyroid carcinomas, TPO protein is expressed, albeit to a more variable extent than normal; when present, TPO in malignant tissues is immunologically normal.

Radiation-induced melanoma-associated leucoderma, systemic antimelanoma immunity and disease-free survival in a patient with advanced-stage melanoma: a case report and immunological analysis

Background  Melanoma is an immunogenic tumour. The development of skin depigmentation or melanoma‐associated leucoderma (MAL) has been associated with favourable clinical outcome in patients with metastatic melanoma, especially after immunotherapy. Evidence for clinically meaningful enhancement of melanoma‐directed autoimmunity, as indicated by MAL, after radiotherapy without immunotherapy has not yet been published.

Demonstration of autoantibodies against tyrosine hydroxylase in patients with alopecia areata

Background  There is strong evidence to suggest that alopecia areata (AA) is a tissue‐specific, T cell‐mediated autoimmune disease, which is usually characterized by patchy areas of hair loss on the scalp. Tyrosine hydroxylase (TH) is a known B‐cell autoantigen in patients with autoimmune polyendocrine syndrome type 1 (APS1) associated with the presence of AA. In addition, melanocyte‐specific proteins, gp100 and MelanA, are putative T‐cell autoantigens in AA and so may also represent targets of the humoral immune response.

Epitopes, avidity and IgG subclasses of tyrosine hydroxylase autoantibodies in vitiligo and alopecia areata patients

Background  We previously detected antibodies against tyrosine hydroxylase (TH) in 23% of patients with nonsegmental vitiligo and in 19% of patients with alopecia areata (AA).