Circulating IgG from a large subset of bullous pemphigoid (BP) patients reacted on immunoblot with a 120-kDa protein in conditioned keratinocyte culture medium and in keratinocyte cell extracts. A protein with a similar molecular weight was recognized by circulating IgA from a subset of patients with linear IgA dermatosis (LAD). Both affinity-purified 120-kDa-specific BP IgG and 120-kDa-specific LAD IgA bound to the roof of salt-split skin. Both proteins recognized are collagenous glycoproteins. Deglycosylation with N-glycosidase F resulted in an identical reduction in molecular weight for both the BP-IgG-recognized protein and the LAD-IgA-recognized protein. Both proteins were equally susceptible to digestion with type VII collagenase. Furthermore, both proteins were absent from conditioned culture medium of keratinocytes from patients with BP180-deficient general atrophic benign epidermolysis bullosa (GABEB). Immunodepletion studies showed that the 120-kDa LAD antigen could be removed from conditioned culture medium by anti-120-kDa BP IgG. Thus these results indicate that these proteins are either highly related or, most probably, identical. A strong antigenic relationship between the 120-kDa protein and the 180-kDa bullous pemphigoid antigen (BP180) was detected by cross-reaction of affinity-purified anti-120-kDa BP patient antibodies to BP180 and cross-reaction of monoclonal anti-180-kDa antibodies to the 120-kDa protein. Notwithstanding this cross-reactivity, the 120-kDa protein also exhibits unique epitopes demonstrated by the nonreactivity of individual anti-120-kDa BP and LAD patient serum with the 180-kDa antigen.

Integrin alpha6beta4 is a hemidesmosomal transmembrane molecule involved in maintaining basal cell-matrix adhesion through interaction of the large intracytoplasmic tail of the beta4 subunit with the keratin intermediate filament network, at least in part through its binding with plectin and BP180/type XVII collagen. Here we report a patient with predominant features of epidermolysis bullosa simplex due to a mutation in the integrin beta4 gene. The patient, a 49-y-old female, had mild blistering of hands and feet from birth on, dystrophy of the nails with onychogryposis, and enamel hypoplasia. She had no alopecia and no history of pyloric atresia. Electron microscopy and antigen mapping of a skin blister revealed that the level of separation was intraepidermal, low in the basal keratinocytes through the attachment plaque of the hemidesmosome. Immuno-fluorescence microscopy revealed absent binding of monoclonal antibody 450-11 A against the third fibronectin III repeat on the intracellular domain of integrin beta4, whereas binding was reduced with monoclonal antibodies recognizing epitopes on amino-terminal and carboxy-terminal ends of the polypeptide. At the molecular level the phenotype was caused by a novel 2 bp deletion 4733delCT in ITGB4, resulting in in-frame skipping of exon 36 and a deduced 50 amino acid deletion (1450-1499) within the third fibronectin type III repeat in the cytoplasmic domain of the integrin beta4 polypeptide. Immunoblot analysis demonstrated a 5 kDa shorter beta4 polypeptide. The 4733delCT mutation was heterozygously present in the DNA. The patient is also expected to be heterozygous for a null allele, as no full-size protein was detected in vitro and the epitope 450-11 A was absent in vivo. These data show that deletion of the third fibronectin type III repeat in the cytoplasmic domain of integrin beta4, which is thought to interact with BP180/type XVII collagen, is clinically pathogenic and results in a mild phenotype with predominant features of epidermolysis bullosa simplex.

This study shows that in a considerable number of supposedly IgG-mediated pemphigus patients IgA to Dsg1 and Dsg3 is also present. In most cases the antigen specificity of the IgA follows the antigen specificity of the IgG, although in a small number of cases IgA is present against the Dsg not recognized by IgG.

This study characterized the high molecular mass BP180 complex that is observed when unheated sodium dodecyl sulfate extracts of human skin or keratinocytes are subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. In heated extracts BP180 is present as a monomer with a molecular weight of 180 kDa, in unheated extracts BP180 runs at a molecular weight position over 500 kDa. By preincubating the unheated extracts at temperatures between 31 degrees C and 40 degrees C, the high molecular weight complex could be "melted" down to monomeric BP180. Under the conditions employed the T1/2 of the dissociation process was between 35 degrees C and 36 degrees C. The temperature resistance of the high molecular weight complex was used to analyze its molecular composition by performing two-dimensional electrophoresis with a "low-temperature" first dimension step and a "high-temperature" second dimension step. Silver staining and immunoblotting of the two-dimensional gels revealed the high molecular weight complex to be composed of solely BP180, indicating that the complex is the nondissociated homotrimeric form of BP180. The 120 kDa linear IgA dermatosis antigen (LAD-1) is an collagenous anchoring filament protein with homology to the extracellular collagenous part of BP180. Two-dimensional immunoblotting showed that LAD-1, as BP180, is also present as a high molecular mass complex and does not form mixed complexes with BP180.

Plectin is a minor pemphigoid antigen with an immunodominant epitope located on the central rod domain.

Primary incubation at room temperature may result in false-negative results in the IgA-BP180 immunoblot assay.

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