Buschman Kerry E, Seraly Mark, Thong H Y, Deng Jau-Shyong, Draviam Rose P, Abernethy John L
Department of Dermatology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
J Cutan Pathol. 2002 May;29(5):282-6. doi: 10.1034/j.1600-0560.2002.290504.x.
Bullous pemphigoid (BP) is an immune-mediated blistering disease, usually characterized immunopathologically by the linear deposition of IgG and C3 along the basement membrane zone (BMZ) of skin. However, positive deposition of C3 but negative staining for IgG on direct immunofluorescence (DIF) studies has been noted in some patients.
Twelve patients known to have BP but with absence of staining for IgG were included in this study. Frozen sections of skin specimens from the 12 patients were subjected to IgG DIF, as well as a sandwich double antibody method of staining for IgG, IgG subclasses, and light chains. Enzyme-linked immunosorbent assay (ELISA) using commercially available human IgG subclasses was used to analyze the subclass restriction of FITC-labeled antihuman IgG conjugates.
Of the 12 skin specimens with positive C3 and negative IgG on DIF, nine were positive for IgG with the double antibody sandwich method. In addition, all 12 specimens had positive linear staining for the subclass IgG4 along the BMZ with this method. There was no IgG light chain restriction. Two commercially obtained antihuman IgG conjugates, both commonly used in our laboratory for DIF testing, were analyzed for separate IgG subclass specificity by ELISA. Both conjugates showed high reactivity to IgG1 and IgG3 with less reactivity to IgG2 and IgG4.
These results suggest that the following factors contribute to false-negative staining for IgG on DIF in some BP patients: (i): subthreshold IgG in skin specimens; (ii) limited reactivity of commercial antihuman IgG conjugates to the IgG4 subclass; and (iii) decreased sensitivity of DIF compared with double antibody methods for the detection of IgG. The use of sandwich double antibody immunofluorescence methods to test for IgG and/or IgG subclasses may be helpful in definitively diagnosing BP in patients with negative IgG and positive C3 staining on DIF.
大疱性类天疱疮（BP）是一种免疫介导的水疱性疾病，通常在免疫病理学上表现为IgG和C3沿皮肤基底膜带（BMZ）呈线性沉积。然而，在一些患者的直接免疫荧光（DIF）研究中，已注意到C3呈阳性沉积但IgG染色为阴性。
本研究纳入了12例已知患有BP但IgG染色阴性的患者。对这12例患者皮肤标本的冰冻切片进行IgG DIF检测，以及用于IgG、IgG亚类和轻链染色的夹心双抗体法检测。使用市售人IgG亚类的酶联免疫吸附测定（ELISA）来分析异硫氰酸荧光素（FITC）标记的抗人IgG缀合物的亚类限制性。
在12例DIF显示C3阳性而IgG阴性的皮肤标本中，9例采用双抗体夹心法检测IgG呈阳性。此外，采用该方法，所有12例标本沿BMZ的IgG4亚类均呈阳性线性染色。不存在IgG轻链限制性。通过ELISA分析了两种实验室常用的市售抗人IgG缀合物对不同IgG亚类的特异性。两种缀合物对IgG1和IgG3的反应性高，对IgG2和IgG4的反应性较低。
这些结果表明，以下因素导致一些BP患者DIF检测IgG出现假阴性染色：（i）皮肤标本中IgG低于阈值；（ii）市售抗人IgG缀合物对IgG4亚类的反应性有限；（iii）与检测IgG的双抗体法相比，DIF的敏感性降低。使用夹心双抗体免疫荧光法检测IgG和/或IgG亚类可能有助于明确诊断DIF检测IgG阴性而C3染色阳性的BP患者。
