A subepidermal blistering dermatosis associated with coexistent IgG and IgA anti-dermal basement membrane zone antibodies; demonstration of IgG antibodies reactive against a 200-kDa dermal antigen

ARTICLE

Subepidermal autoimmune bullous diseases that show circulating antibodies reacting to the dermal side of salt split skin in indirect immunofluorescense (IF) test include linear IgA bullous dermatosis (LABD) of sublamina densa type, anti-laminin 5 cicatricial pemphigoid (CP), and epidermolysis bullosa acquisita (EBA).

Recently, several authors have reported a subepidermal blistering disease associated with IgG autoantibodies reactive to a novel 200-kDa dermal protein of the basement membrane zone (BMZ) [1-8], although antigenic material has not been characterized at a molecular level. This target antigen appears to localize within the lamina lucida, but is different from laminin 5, and type VII collagen [8]. The uncharacterized 200-kDa epidermal protein was detected as a target autoantigen also in LABD [9].

Zillikens et al. [8] proposed the designation of anti-p200 pemphigoid for this bullous dermatosis, based on the clinical resemblance of most reported cases to bullous pemphigoid (BP). By indirect IF study on salt split skin, immunological findings in anti-p200 pemphigoid are clearly different from BP. The former shows a dermal staining pattern, while the latter demonstrates an epidermal staining pattern.

We report here a unique case of this bullous dermatosis that showed coexistence of circulating IgG and IgA antibodies reactive to the dermal side of salt split skin, with the IgG antibodies recognizing a 200-kDa dermal antigen. The present patient was clinically and histologically similar to the previously reported cases, but was different from them in the immunological characteristics and in the resistance to conventional therapy.

Case report

A 66-year-old Japanese woman with a three-month history of pruritic eruptions was referred to us in March 1998. On examination, there were annular erythematous lesions associated with vesicles scattered mainly on the trunk, forearms and thighs. The erythematous lesions presented a target-like appearance reminiscent of erythema multiforme and annular erythema (Fig. 1). The oral, ocular, and genital mucous membranes were not affected. The skin lesions healed leaving milia but without scar formation. The patient had been treated with celiprolol hydrochloride and disopyramide for arrhythmia (transient ventricular tachycardia) over the past 16 years. However, her clinical course was not affected by discontinuation of these drugs.

Laboratory findings including a complete blood count, liver and renal function tests were all within normal limits except for a slightly elevated erythrocyte sedimentation rate, 17 mm/hr. An antinuclear antibody was negative.

A skin biopsy specimen obtained from an early erythematous lesion with a small vesicle on the right forearm showed a subepidermal blister with microabscesses of neutrophils. Eosinophils were absent (Fig. 2).

Direct IF of an early erythematous lesion revealed IgG, IgA and C3 deposition in a linear pattern at the BMZ. The deposits of IgA appeared more intense than those of IgG. Indirect IF using normal human skin as a substrate demonstrated the presence of IgG and IgA antibodies reactive to the BMZ, both at a titer of 1:160. Indirect IF with 1.0 mol/l NaCl split skin demonstrated that IgG and IgA antibodies reacted to the dermal side of the salt split skin (Fig. 3), and IgA antibodies also bound, with relatively weak intensity, to the epidermal side. However, the reactivity of IgA antibodies to the epidermal side was no longer detectable when we examined the patient one year later. Electron microscopy of an early bullous lesion revealed a cleft beneath the basal lamina (not shown).

Immunoblot analysis of the serum was performed using EDTA-separated normal human epidermal extracts [10] and EDTA-separated normal human dermal extracts [11]. Our patient's IgG antibodies showed no specific reactivity against the epidermal extracts, including 180-kDa and 230-kDa BP antigens, or against a recombinant protein corresponding to the BP180 NC16a domain [12]. The IgG antibodies reacted exclusively with a 200-kDa dermal protein (Fig. 4). This serum sample did not show any reactivity with the 290-kDa protein (type VII collagen) which is the target antigen of EBA. Our patient's IgA antibodies showed no specific reactivity against the epidermal extracts, including 180-kDa and 230-kDa BP antigens. At first the patient's IgA class antibodies reacted faintly with a recombinant protein of the BP180 NC16a domain, but this reactivity disappeared later. These immunological findings are summarized in Table I.

The patient's eruption was controlled with dapsone 50- 100 mg, betamethasone 0.5-0.75 mg and tetracycline 200 mg daily together with twice a day applications of 0.12% betamethasone-17-valerate ointment for the first five months. Subsequently, the lesions gradually worsened, becoming unmanageable even with oral prednisone 30 mg and dapsone 100 mg a day for over one month. Therefore, we tried plasmapheresis therapy in addition to oral prednisone and dapsone. Three cycles of plasma exchanges in a week were performed, followed by 3 cycles at intervals of 1-3 weeks. With this therapy, the dose of prednisone could be gradually tapered. Three years after the onset, the patient's skin lesions developed only intermittently with betamethasone 1 mg and dapsone 25 mg daily.

Discussion

Recently, a subepidermal autoimmune blistering disease against a novel 200-kDa dermal protein has been described by several authors [1-8], as summarized in Table II. The clinical appearance was similar to that of BP [1, 2, 6, 7], dermatitis herpetiformis [4] or linear IgA bullous dermatosis [5]. Moreover, psoriasis was reported to be associated in two cases [2, 3]. Mucosal involvement was also observed [1, 5]. Skin lesions healed with milium formation but without any scarring. Almost all these cases responded to treatment with dapsone [6], cyclosporin [2], corticosteroids [1, 4, 6], tetracyclines [1], combination of tetracyclines and niacinamide [7], colchicine [1], or topical application of corticosteroids alone [3]. Despite some similarities to the reported cases, our first combination therapy of corticosteroids, dapsone and tetracyclines was not so effective in our patient. Because of the difficulty in managing the patient's eruptions, we eventually tried plasmapheresis. Subsequently, the skin lesions gradually improved and we could taper the oral corticosteroid dose. Therefore, our case shared some of the clinical features with EBA, such as the poor response to conventional treatments and long lasting disease course. However, the antibodies of our patient did not recognize the 290-kDa dermal antigen of EBA, and the patient's lesions healed without scars.

In all the previously reported cases of subepidermal blistering disease with autoantibodies to the 200-kDa dermal autoantigen, circulating antibodies binding to the dermal side of salt split skin were of the IgG class alone. In contrast, our present case showed both IgG and IgA antibodies demonstrating a strong positive reaction to the dermal side of salt split skin. Recently, it has been increasingly reported that the patient's serum of various autoimmune bullous dermatoses had circulating IgA autoantibodies in addition to IgG autoantibodies, which reacted against the 180-kDa BP antigen in BP and CP [13] and against desmoglein 3 in active pemphigus vulgaris [14]. The significance of these IgA autoantibodies remains to be elucidated.

In our case presenting circulating IgG and IgA antibodies reactive with the dermal side of salt split skin, only the IgG antibodies directed against the 200-kDa dermal protein were observed by immunoblot analysis. We failed to detect IgA antibodies reactive to the 200-kDa antigen or to any other specific dermal antigen. This negative result might be explained by the difference in sensitivity between IF test and immunoblotting analysis. As another possibility, we cannot rule out the requirement of a warmer primary incubation temperature in immunoblot, as recently described by Pas et al. [15]. Although we were unable to ascertain whether both IgG and IgA antibodies of the patient's serum recognize the same 200-kDa dermal antigen or not, the finding of coexisting IgA and IgG antibodies to the dermal BMZ remains of note. In addition, our case was unique in that the IgA antibodies also had immunological characteristics of BP. In some of the previous cases, patient's serum samples were reported to weakly react with 230-kDa BP antigen [2] and 180-kDa BP antigen [4] by immunoblot analysis. Our patient's IgA antibodies faintly stained the epidermal side of the salt split skin, and showed weak reactivity with NC16a domain of the 180-kDa BP antigen recombinant protein by immunoblot analysis. We cannot exclude the possibility that these antibodies may be secondarily induced during the clinical course by the damage to BMZ.

CONCLUSION

In conclusion, we report here a unique case showing coexistent circulating IgG and IgA antibodies binding to the dermal side of BMZ, and IgG antibodies specific for a novel 200-kDa dermal antigen.

Acknowledgements

We thank Pr. T. Hashimoto, Department of Dermatology, Kurume University School of Medicine, for his helpful assistance with IF and immunoblotting studies, and Dr. Y. Mistuhashi, Department of Dermatology, Yamagata University School of Medicine, for his help with IF studies and kind diagnostic advice.

Article accepted on 8/8/02

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