Desmoyokin/AHNAK protein localizes to the non-desmosomal keratinocyte cell surface of human epidermis

Desmoyokin, a high-molecular-weight protein of 680 kD with a 170-nm-long dumbbell shape, was originally thought to be localized to the desmosomal attachment plaque and to work as a kind of stabilizer of desmosomes. Recently, desmoyokin was shown to be widely detected in many types of cells that do not possess desmosomes. The purpose of the present study was to elucidate the precise localization and possible function of desmoyokin in human epidermis. In 0.2-micron ultrathin cryosections of human skin for immunofluorescence, anti-desmoyokin antibody showed a ladder-like staining pattern along the cell surface, whereas anti-desmocollin and anti-desmoplakin antibodies as controls showed a discontinuous dotted staining pattern, indicating their distinct localization. Post-embedding immunoelectron microscopy with cryofixation and cryosubstitution revealed that desmoyokin was localized mainly along the non-desmosomal and non-hemidesmosomal plasma membrane, but not to the desmosomes and hemidesmosomes themselves. This localization was further confirmed by double-labeling immunoelectron microscopy with antibodies against desmocollin, desmoplakin, or bullous pemphigoid antigen. Results indicate that desmoyokin was not localized to the desmosomes themselves as previously considered. Desmoyokin was localized to the non-desmosomal and non-hemidesmosomal epidermal keratinocyte cell surface as a plasma membrane-associated protein, and might play a role in cell adhesion that is not directly associated with desmosomes or hemidesmosomes.

Autoantibodies from patients with cicatricial pemphigoid target different sites in epidermal basement membrane

Indirect immunogold electron microscopy studies of cryofixed, freeze-substituted, and post-embedded normal human skin were performed to localize precisely the ultrastructural binding site of circulating autoantibodies from two groups of patients with cicatricial pemphigoid. One group of patients had circulating IgG autoantibodies that bound the dermal side of 1 M NaCl-split skin and immunoprecipitated epiligrin. The other group of patients had circulating IgG autoantibodies directed against the epidermal side of 1 M NaCl-split skin and showed no specific reactivity to any keratinocyte polypeptide by immunoprecipitation. IgG autoantibodies from all patients with anti-epiligrin cicatricial pemphigoid bound the lowermost aspect of the lamina lucida at its interface with the lamina densa; the greatest staining was seen beneath and beside hemidesmosomes. In contrast, IgG from cicatricial pemphigoid patients whose autoantibodies bound the epidermal side of 1 M NaCl-split skin localized to hemidesmosomes and the junction between hemidesmosomes and the plasma membranes of basal keratinocytes. Although the latter staining pattern is similar to that observed with anti-BPAG2 autoantibodies, sera from our patients with cicatricial pemphigoid did not bind BPAG2 in immunoprecipitation studies of radiolabeled human keratinocyte extracts or show immunoblot reactivity to a fusion protein corresponding to the immunodominant epitope of this polypeptide. These studies demonstrate the following: 1) Autoantibodies from patients with anti-epiligrin cicatricial pemphigoid consistently bind the lower lamina lucida at its interface with the lamina densa; and 2) other patients with the same phenotype may have IgG autoantibodies against yet-unknown epitopes in basal keratinocytes.

A Japanese case of the fibrillar type of dermatitis herpetiformis

BACKGROUND

Although dermatitis herpetiformis (DH) is a relatively common disease in Caucasian populations, this disease is very rare in Asian populations including the Japanese.

METHODS AND RESULTS

We present a Japanese DH patient, who showed a fibrillar pattern of deposition of IgA, IgG, IgM and C3. The HLA typing revealed no B8/DR3. The survey of the Japanese literature and the comparison to studies on American or European DH revealed several interesting differences: high frequency of the fibrillar pattern, relatively high incidence of deposits of immunoglobulins other than IgA, rarity of gluten-sensitive enteropathy and HLA-B8/DR3 in Japanese DH.

CONCLUSION

The present study suggests that there may be a significant difference in pathophysiology between Caucasian and Japanese DH patients.

Paraneoplastic pemphigus: the first case report from Japan

Paraneoplastic pemphigus is a rare skin disease characterized by painful mucosal ulcerations and polymorphous skin lesions in association with an underlying neoplasm. A 54-year-old Japanese man, who had received chemotherapy and radiation therapy due to a diagnosis of non-Hodgkin's lymphoma, developed marked stomatitis, conjunctivitis and blisters. Histologic examination showed suprabasal cleft formation with acantholysis and keratinocyte necrosis. Direct immunofluorescence revealed the deposition of IgG at the cell surface of the keratinocytes and C3 at the basement membrane zone. Indirect immunofluorescence on normal human skin and rat bladder sections revealed circulating autoantibodies to the cell surface of both keratinocytes and transitional epithelia. Immunoprecipitation disclosed antibodies reactive to the 250-kD, 230-kD, 210-kD and 170-kD proteins. From these results, a diagnosis of paraneoplastic pemphigus was made. This is the first report of paraneoplastic pemphigus from Japan.

A case of bullous pemphigoid with antidesmoplakin autoantibodies

Paraneoplastic pemphigus, a recently identified disease entity, is associated with autoantibodies against a variety of epidermal proteins including desmoplakins I and II, and the 230-kDa bullous pemphigoid (BP) antigen. We report an 84-year-old Japanese man who had typical clinical and histopathological features of BP, but in whom indirect immunofluorescence, using normal human skin as the substrate, revealed concomitant serum antibasement membrane zone and antikeratinocyte cell surface autoantibodies. His serum showed reactivity similar to that which is seen with antidesmoplakin monoclonal antibody on immunofluorescence of cardiac muscle and urinary bladder. With immunoblotting, using various antigen sources, the patient's serum reacted with desmoplakins I and II, and with both the 230- and 180-kDa BP antigens. Immunogold electron microscopy also indicated the presence of antidesmoplakin antibodies. Although the significance of the antidesmoplakin antibodies in this patient is unknown, the findings in this case may provide an insight into understanding the occurrence of antidesmoplakin antibodies in paraneoplastic pemphigus.

Prenatal diagnosis of tyrosinase-negative oculocutaneous albinism by an electron microscopic dopa reaction test of fetal skin

An electron microscopic DOPA reaction test of fetal skin was used for the prenatal diagnosis of tyrosinase-negative oculocutaneous albinism (OCA). The subject was a 34-year-old Japanese woman in her second pregnancy. Her first child, born in 1982, had been previously examined and confirmed to have tyrosinase-negative OCA. The parents requested a prenatal diagnosis and we sampled skin from the upper trunk of the fetus. On conventional electron microscopy, the development of melanosomes in interfollicular melanocytes had progressed no further than stage II. Fetal skin samples incubated with L-DOPA solution indicated a lack of tyrosinase activity and showed that the melanosomes had not progressed beyond stage II. In skin samples from the trunks of three Japanese fetuses aborted for other reasons at 19-20 weeks of gestation, most premature melanosomes were further melanized to stage IV after incubation with L-DOPA solution. A prenatal diagnosis of tyrosinase-negative OCA was made. The parents requested a termination and skin biopsies of the abortus confirmed the diagnosis. This study shows that tyrosinase is normally present in melanocytes of the fetal epidermis at 20 weeks' gestation, and that the electron microscopic DOPA reaction test of a fetal skin biopsy specimen is safe and practical, and provides reliable information for making a prenatal diagnosis of tyrosinase-negative OCA in the second trimester.

Difference in binding sites of autoantibodies against 230- and 170-kD bullous pemphigoid antigens on salt-split skin

The purpose of this study is to clarify a relationship between bullous pemphigoid autoantibodies against two major BP antigens, 230 kilodalton (kD) (BPAG1) and 180 kD (BPAG2) and their binding sites, using immunoblot analysis and indirect immunofluorescence on salt-split skin. Of the 135 sera obtained from patients in whom bullous pemphigoid had previously been diagnosed by clinical and immunopathologic criteria, all 52 sera recognizing only BPAG1 stained only the epidermal side of split skin (epidermal pattern). Of 24 sera recognizing only BPAG2, 20 showed the epidermal pattern and four stained both the epidermal and dermal sides (combined pattern). Of 42 recognizing both BPAG1 and BPAG2, 35 showed the epidermal pattern and seven showed the combined pattern. Of 17 that reacted with neither antigen, nine showed the epidermal pattern, four showed the combined pattern, and four stained only the dermal side (dermal pattern). Two of the four cases that showed a dermal pattern were retrospectively identified as epidermolysis bullosa acquisita. Immunoelectron microscopy confirmed that a serum with combined pattern bound to both intracellular and extracellular sites of hemidesmosomes. Our results suggest that autoantibodies that react solely with BPAG1 bind exclusively to the epidermal side of salt-split skin and never show either a combined or a dermal pattern, and that most antibodies against BPAG2 bind to the epidermal side. The combined pattern suggests the presence of autoantibodies against the extracellular epitopes of BPAG2 that are separated from the epidermis during the salt-splitting process.

Demonstration of desmosomal antigens by electron microscopy using cryofixed and cryosubstituted skin with silver-enhanced gold probe

In a previous post-embedding immunogold electron microscopic (EM) studies, localization of various desmosomal antigens was possible at high but not at low magnification. We developed a method for simultaneous demonstration of epidermal desmosomal antigens at both low- and high-power EM magnifications by a method based on cryofixation and acetone cryosubstitution and the use of a 1-nm gold probe with silver enhancement. Ultra-thin sections of Lowicryl K11M were incubated with primary antibodies against desmoplakin, desmocollin, or desmoglein, followed by 1-nm gold-conjugated secondary antibody. Silver enhancement for 12 min provided the ideal labeling size for low-power visualization, whereas silver enhancement for 4-6 min was ideal for high-power EM observation. Each desmosome immunolabeled with the gold probe was clearly demonstrated, even at very low-power magnification. The level of background labeling could be determined easily and the area of interest for high-power observation selected accurately. The fine ultrastructural appearance of desmosomal molecules was precisely demonstrated on high-power observation. This system should be useful for the immunocytochemical study of a variety of desmosomal antigens as well as other molecules of interest.

A case of bullous pemphigoid with antidesmoplakin autoantibodies

We present an 84-year-old Japanese male showing typical features of bullous pemphigoid (BP). However, immunofluorescence of normal human skin sections revealed concurrent anti-basement-membrane-zone and anti-keratinocyte-cell-surface autoantibodies in the serum. With immunoblotting, the patient's serum reacted with desmoplakins I and II, as well as with both the 230-kD and the 180-kD BP antigens. The studies for this case may provide us with an insight to understand the occurrence of antidesmoplakin antibodies in paraneoplastic pemphigus.

Is tubular apocrine adenoma a distinct clinical entity?

A 75-year-old Japanese man developed a tubular apocrine adenoma (TAA) (tubulopapillary hidradenoma with apocrine differentiation, a rare skin tumor), within a long-standing organoid nevus on the parietal area of his scalp. Histologically, the tumor consisted of dilated ductlike areas with some atypism and apocrine glandlike areas surrounded by myoepithelial cells. The superficial part of the tumor was connected to the epidermis and showed some of the characteristics of syringocystadenoma papilliferum (SCAP). The close relationship between TAA, SCAP, and papillary eccrine adenoma (PEA) is discussed. According to 19 reported cases of TAA, SCAP might occur together with TAA when they are preceded by an organoid nevus, and they might represent a spectrum of disease. Although TAA and PEA may represent another spectrum (designated as tubulopapillary hidradenoma), the relationship to SCAP should be considered in understanding and diagnosing an intermediate case.

Malignant epithelioid schwannoma of the skin showing partial HMB-45 positivity

A malignant epithelioid schwannoma occurred on the right second toe of a 30-year-old Japanese man. It was a firm, flesh-colored, benign-appearing nodule and measured 13 x 9 mm in diameter and 6 mm in height. To our knowledge, this is the first case of malignant epithelioid schwannoma occurring on the toe. Histopathology was characterized by a circumscribed nodule in the dermis that predominantly consisted of atypical large epithelioid cells with some spindle cells whose proliferation was similar to that of the Verocay bodies seen in ordinary schwannoma. Fontana-Masson staining demonstrated no melanin pigment in the tumor at the light microscopic level. The eosinophilic cytoplasm contained abundant glycogen and was positive for S-100 protein and HMB-45, as usually seen in melanomas. Electron microscopy revealed that there was an abundance of long-spacing collagen in the extracellular matrix, and the cells contained numerous dense-cored granules. But no definite melanosomes were observed in any stage. As far as we are aware, this is the first case of a malignant epithelioid schwannoma showing HMB-45 positivity.

Human autoantibodies against the 230-kD bullous pemphigoid antigen (BPAG1) bind only to the intracellular domain of the hemidesmosome, whereas those against the 180-kD bullous pemphigoid antigen (BPAG2) bind along the plasma membrane of the hemidesmosome in normal human and swine skin

Bullous pemphigoid (BP) is a blistering skin disease in which autoantibodies develop to hemidesmosomal components of the epidermal basement membrane zone, including two major antigenic proteins of the 230-kD antigen (BPAG1) and the 180-kD antigen (BPAG2). The present study demonstrated the precise ultrastructural localization of the epitopes for autoantibodies against BPAG1 and BPAG2 in normal skin. Autoantibodies against either BPAG1 or BPAG2 were affinity-purified using nitrocellulose membrane, which was blotted with SDS-PAGE-fractionated antigens from human epidermal extract as the immunoabsorbent. Postembedding, immunogold electron microscopy was performed after skin was processed by rapid freezing and freeze substitution fixation without chemical fixatives. Purified autoantibodies against BPAG1 bound only to the intracellular domain of the hemidesmosome, and 80% of the gold labeling was within 40-140 nm from the plasma membrane (mean distance 91 nm inside). In contrast, the autoantibodies against BPAG2 bound along the plasma membrane of the hemidesmosome, and 80% of the gold labeling was within 10 nm outside to 50 nm inside the cells (mean distance 12 nm inside). These results suggest that the autoantibodies against BPAG1 and BPAG2 react with the epitopes localizing in distinct regions of the hemidesmosome complex, and may play different roles in the blister formation in patients with BP.

Comparative study of bullous pemphigoid antigens among Japanese, British, and U.S. patients indicates similar antigen profiles with the 170-kD antigen present both in the basement membrane and on the keratinocyte cell membrane

There are a number of controversies relating to studies of bullous pemphigoid (BP) antigens from different institutions, mainly regarding the detection of the 230-kD and 170-kD BP antigens. In this study, in an attempt to resolve the discrepancies, we have examined and compared the reactivity by immunofluorescence, immunoblotting, and immunoprecipitation among the sera from Japanese, British and U.S. BP patients. Both the 230-kD and 170-kD BP antigens were detected by various sera from all populations with immunoblotting, whereas immunoprecipitation detected only the 230-kD BP antigen but not the 170-kD BP antigen. Immunoprecipitation was more sensitive than immunoblotting to detect the 230-kD antigen. These results indicate that both the 230-kD and 170-kD proteins are BP antigens found in all three populations. By immunofluorescence cell surface staining in the lower epidermis in addition to basement membrane zone staining was shown by a considerable number of patients' sera in all populations. Comparison between the results of immunofluorescence and immunoblotting revealed a clear correlation of this cell surface staining with the presence of antibodies against the 170-kD BP antigen. That the affinity-purified antibodies specific to the 170-kD BP antigen showed this cell surface staining further confirmed this correlation. These results may indicate a different nature of the 170-kD BP antigen from that of the 230-kD BP antigen.