Z Liu

Medical College of Wisconsin, Milwaukee, Wisconsin, United States

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Publications (11)66.18 Total impact

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    ABSTRACT: Pemphigus vulgaris (PV) is a dermatosis mediated by autoantibodies against desmoglein 3 (Dsg3). It was known that intraperitoneal (i.p.) injections of PV IgG and PV F(ab')2, but not of PV Fab, into neonatal mice reproduced the key features of the disease in these animals. It was proposed that crosslinking of antigen by bivalent PV autoantibodies may trigger acantholysis in PV. In the present study, we have used subcutaneous (s.c.) injections of PV IgG and its proteolytic fragments into neonatal mice to test equimolar amounts of these autoantibody fractions. Mice developed clinical and histological features of PV in a dose-dependent manner following a similar time course. PV IgG and Fab fractions induced acantholysis as early as 2 hr after the injection. It was also demonstrated that sc injections of PV Fab were more effective in inducing disease than ip injections. PV autoantibodies may bind an "adhesive site" of Dsg3 and impair its function, thus triggering acantholysis.
    Clinical Immunology and Immunopathology 11/1997; 85(1):90-6. DOI:10.1006/clin.1997.4408
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    ABSTRACT: Bullous pemphigoid (BP) is an inflammatory subepidermal blistering disease associated with an IgG autoimmune response to the hemidesmosomal protein, BP180. Using a passive transfer mouse model, our group has shown previously that antibodies to the murine BP180 (mBP180) ectodomain are capable of triggering a blistering skin disease that closely mimics human BP. In this study, we investigated the role of neutrophils in the immunopathogenesis of this disease model. BALB/c mice depleted of circulating neutrophils by treatment with neutrophil-specific antibodies were no longer susceptible to the pathogenic effects of anti-mBP180 IgG. IgG and complement were deposited at the dermal-epidermal junction of these animals, but there was no evidence of inflammatory infiltration or blistering. C5-deficient mice, which are resistant to the pathogenic activity of anti-mBP180 IgG, could be made susceptible to this IgG-mediated blistering disease by intradermal administration of a neutrophil chemoattractant, IL-8 or C5a. Intraperitoneal injection of IL-8, which sequesters neutrophils in the peritoneal cavity, interferes with anti-mBP180-induced neutrophilic infiltration of the skin and prevented the development of BP disease in BALB/c mice. These findings provide the first direct evidence that neutrophils recruited to the skin via a C5-dependent pathway play an essential role in subepidermal blister formation in experimental BP, and suggest new directions for disease intervention.
    Journal of Clinical Investigation 10/1997; 100(5):1256-63. DOI:10.1172/JCI119639 · 13.77 Impact Factor
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    ABSTRACT: Epidermal blister formation is the hallmark of three cutaneous autoimmune diseases: pemphigus foliaceous (PF), pemphigus vulgaris (PV) and bullous pemphigoid (BP). In PF and PV, blistering is due to acantholysis (cell-cell detachment) in the subcorneal and suprabasal epidermal layers, respectively, while BP is characterized by detachment of the basal epidermal cells from the underlying dermis. For several years, we have focused our research efforts on elucidating the pathogenic mechanisms operating in these bullous diseases. Early studies performed by our research group and others revealed that in all three diseases, the patients produce autoantibodies that bind to target antigens located on the surface of cells that are undergoing detachment. Thus it was hypothesized that these anti-epidermal autoantibodies played a role in initiating blister formation. We recognized that elucidating the normal mechanisms of epidermal cell-cell and cell-dermis adhesion would help us understand the abnormal epidermal cell detachment seen in these patients. We hypothesized that under normal conditions these adhesive mechanisms in the epidermis are complex and dynamic and mediated by the interaction of cell surface molecules unique to each layer of the epidermis. Also, we postulated that PV, PF and BP autoantibodies may cause cell detachment by impairing the function of their respective epidermal cell surfaces. Support for this hypothesis has come from recent studies which showed that PV and PF autoantibodies recognize distinct, yet related, desmosomal glycoproteins in the cadherin family of calcium-dependent adhesion molecules. The epidermal antigen in PV is desmoglein-3 (dsg3), while in PF it is desmoglein-1 (dsg1). These anti-epidermal autoantibodies have been shown to be pathogenic in passive transfer experiments. Neonatal mice injected with these antibodies develop intraepidermal blisters characteristic of the corresponding human disease. Autoantibodies in BP react with BP180 and BP230, two major components of the hemidesmosome, a cell structure involved in dermal-epidermal adhesion. Recent passive transfer mouse model studies performed in our laboratory have shown that anti-BP180 antibodies can induce subepidermal blistering in the experimental animals. Moreover, the pathogenic mechanism was shown to be dependent on complement activation and recruitment of neutrophils to the dermal-epidermal junction. In conclusion, desmosomal glycoproteins are the targets of autoimmune injury in PV and PF. The anti-epidermal autoantibodies may cause intraepidermal blisters by impairing the function of dsg1 and dsg3. In BP the hemidesmosome is the target. It appears that antiBP180 antibodies cause subepidermal blister formation by triggering a complement- and neutrophil-mediated inflammatory process.
    Clinical & Experimental Immunology 02/1997; 107 Suppl 1:9-15. · 3.28 Impact Factor
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    ABSTRACT: A novel member of the ubiquitin carrier protein family, designated E2EPF, has been cloned by our laboratory and expressed in a bacterial system in an active form. Ubiquitin carrier proteins, or E2s, catalyze one step in a multistep process that leads to the covalent conjugation of ubiquitin to substrate proteins. In this paper, we show that recombinant E2EPF catalyzes auto/multiubiquitination, the conjugation of multiple ubiquitin molecules to itself. Multiubiquitination has been shown previously to be required for targeting of a substrate protein for rapid degradation. Using a rabbit reticulocyte lysate system, E2EPF was shown to support the degradation of a model substrate in an ATP- and ubiquitin-dependent fashion. In contrast to a previous study which showed that selective protein degradation in one system is dependent upon multiubiquitination via the lysine 48 residue of ubiquitin, multiubiquitination, and proteolytic targeting by E2EPF was shown here to be independent of the lysine 48 multiubiquitin linkage. This functional characterization of E2EPF revealed a combination of features that distinguishes this enzyme from all previously characterized members of the ubiquitin carrier protein family. These results also suggest several possible autoregulatory models for E2EPF involving auto- and multiubiquitination.
    Journal of Biological Chemistry 03/1996; 271(5):2817-22. DOI:10.1074/jbc.271.5.2817 · 4.60 Impact Factor
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    ABSTRACT: Bullous pemphigoid (BP) and herpes gestationis (HG) are subepidermal blistering diseases associated with an autoimmune response directed against BP180, an epidermal hemidesmosomal glycoprotein. The pathogenic relevance of this Ag/Ab system was established by the recent demonstration that IgG Abs reactive with the murine form of BP180 (mBP180) are capable of triggering a subepidermal blistering disease after passive transfer into neonatal BALB/c mice. The aim of the present study was to determine the fine specificity of the pathogenically relevant Abs in this experimental model of BP. Four high titer rabbit-anti-mBP180 antisera were included in this analysis--only two of which exhibited pathogenic activity in the passive transfer model. Immunoblot analysis using a panel of mBP180 deletion mutants revealed that each of the four rabbit sera reacted with at least three distinct sites on the mBP180 ectodomain; however, this technique failed to distinguish between the reactivity patterns of the pathogenic and nonpathogenic sera. An alternative technique, liquid phase immunoadsorption analysis, was used to identify one mBP180 antigenic site, comprising 9 to 12 amino acids and designated mBP1, that was specifically recognized by the two pathogenic sera. Pre-adsorption of pathogenically active IgG preparations with fusion proteins containing the mBP1 antigenic site resulted in complete blocking of immunofluorescence reactivity with the murine basement membrane zone (BMZ) and in complete neutralization of pathogenic activity. Anti-BMZ reactivity displayed by nonpathogenic Abs was not altered or diminished by pre-adsorption with this same mBP180 recombinant protein. These findings should help to elucidate the immunopathologic mechanisms responsible for human BP and HG and may have significant implications in the diagnosis and treatment of these autoimmune diseases.
    The Journal of Immunology 01/1996; 155(11):5449-54. · 5.36 Impact Factor
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    ABSTRACT: BP is an organ-specific autoimmune disease characterized by blistering of the skin due to a detachment of the epidermis from the underlying connective tissue layer and by the production of autoantibodies directed against the cutaneous basement membrane zone. A 180-kD epidermal protein, BP180, has been identified as one of the major antigenic targets of these autoantibodies and, interestingly, has been localized to the epidermal hemidesmosome, a cellular structure involved in anchoring basal epithelial cells to the basement membrane. An immunodominant and potentially pathogenic epitope associated with BP has recently been mapped by our laboratory to a site on the extracellular domain of the human BP180 antigen. This antigenic site, designated the MCW-1 epitope, has been shown to be recognized by the majority of sera from patients with either BP or HG, a pregnancy-associated subepidermal bullous disease. Unfortunately, the MCW-1 epitope is absent from the murine BP180 molecule; therefore, human autoantibodies directed against this site could not be tested directly for pathogenicity using the conventional passive transfer mouse model. As an alternative approach, rabbit antibodies were prepared against the segment of murine BP180 that is homologous with the MCW-1 epitope region and were tested for pathogenicity by passive transfer experiments. Remarkably, neonatal mice injected with these antibodies developed a subepidermal blistering disease that faithfully reproduced all of the key immunopathological features of BP and HG--deposition of lgG and complement at the dermal-epidermal junction, inflammatory infiltration of the upper dermis, and frank, subepidermal blistering. These results strongly suggest that the autoimmune response against the human BP180 MCW-1 epitope is relevant in the pathogenesis of blister formation in BP and HG patients. This animal model is currently being used to further dissect the pathophysiology of these autoimmune disorders.
    Proceedings of the Association of American Physicians 08/1995; 107(2):237-41.
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    ABSTRACT: Bullous pemphigoid (BP) is a blistering skin disease associated with an IgG autoimmune response directed against the ectodomain of the hemidesmosomal protein, BP180. An animal model of BP has recently been developed by our laboratory based on the passive transfer of rabbit antimurine BP180 antibodies into neonatal BALB/c mice. The experimental animals develop a blistering disease that reproduces all of the key immunopathological features of BP. In the present study we have investigated the role of complement in the pathogenesis of subepidermal blistering in the mouse model of BP. We demonstrate the following. (a) Rabbit anti-murine-BP180 IgG was effective in inducing cutaneous blisters in a C5-sufficient mouse strain, but failed to induce disease in the syngeneic C5-deficient strain; (b) neonatal BALB/c mice, pretreated with cobra venom factor to deplete complement, became resistant to the pathogenic effects of the anti-BP180 IgG; (c) F(ab')2 fragments generated from the anti-BP180 IgG exhibited no pathogenic activity in the mouse model; and (d) histologic evaluation of the skin of mice described in points b and c above showed minimal or no neutrophilic cell infiltration in the upper dermis. Thus, anti-BP180 antibodies trigger subepidermal blistering in this BP model via complement activation. This experimental model of BP should greatly facilitate future studies on the pathophysiology of autoantibody-mediated diseases of the dermal-epidermal junction.
    Journal of Clinical Investigation 05/1995; 95(4):1539-44. DOI:10.1172/JCI117826 · 13.77 Impact Factor
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    ABSTRACT: An immunodominant and potentially pathogenic epitope associated with bullous pemphigoid (BP) and herpes gestationis (HG) has recently been mapped by our laboratory to a noncollagenous stretch of the extracellular domain of the human BP180 antigen. This antigenic site, designated the MCW-1 epitope, has been shown to be recognized by the majority of BP and HG sera. Interestingly, the MCW-1 epitope is absent from the murine BP180 molecule, and therefore, human autoantibodies directed against this site could not be tested for pathogenicity using the conventional passive transfer mouse model. Alternatively, rabbit antibodies were prepared against recombinant forms of the human MCW-1 epitope and the murine NC16A domain and were tested for pathogenicity by passive transfer experiments. Neonatal mice injected with rabbit antimurine BP180 IgG developed a subepidermal blistering disease that closely mimicked BP and HG at the clinical, histological and immunological levels. Rabbit IgG specific for the human MCW-1 epitope was not pathogenic. These results suggest that the autoantibodies against the MCW-1 epitope of the human BP180 antigen found in BP and HG sera may be relevant in the pathogenesis of blister formation in these patients.
    Dermatology 02/1994; 189 Suppl 1:34-7. DOI:10.1159/000246925 · 1.69 Impact Factor
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    ABSTRACT: Subepidermal blistering associated with the human skin diseases bullous pemphigoid and herpes gestationis has been thought to be an IgG autoantibody-mediated process; however, previous attempts to demonstrate the pathogenicity of patient autoantibodies have been unsuccessful. An immunodominant and potentially pathogenic epitope associated with these blistering diseases has recently been mapped to the extracellular domain of a human epidermal antigen, BP180. Patient autoantibodies that react with this well-defined antigenic site failed to crossreact with the murine form of this autoantigen and thus could not be assayed for pathogenicity in a conventional passive transfer mouse model. As an alternative, rabbit polyclonal antibodies were generated against a segment of the murine BP180 protein homologous with the human BP180 autoantibody-reactive site and were passively transferred into neonatal BALB/c mice. The injected animals developed a subepidermal blistering disease that closely mimicked bullous pemphigoid and herpes gestationis at the clinical, histological, and immunological levels. Autoantibodies that recognize the human BP180 ectodomain are therefore likely to play an initiatory role in the pathogenesis of bullous pemphigoid and herpes gestationis.
    Journal of Clinical Investigation 12/1993; 92(5):2480-8. DOI:10.1172/JCI116856 · 13.77 Impact Factor
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    ABSTRACT: Bullous pemphigoid (BP) and herpes gestationis (HG) are skin diseases characterized by subepidermal blisters and autoantibodies against two hemidesmosomal Ag, i.e., BP230 and BP180. Based on sequence analysis the BP180 Ag was predicted to be a transmembrane protein with a long extracellular collagenous domain. In the present investigation fusion proteins encompassing various segments of the BP180 Ag were expressed in a prokaryotic system and assayed by immunoblotting and immunoadsorption against a panel of BP, HG and control sera. One antigenic site, comprising 14 amino acids of the BP180 noncollagenous (NC) 16A domain, was shown to be recognized by 60% of BP sera and by 63% of HG sera tested. 73% (11/15) of BP sera and 100% (8/8) of HG sera reacted with at least one of three BP180 fusion proteins representing various portions of the NC16A domain. Immunoadsorption analysis identified this region of BP180 as an immunodominant site. Using an affinity purified rabbit antiserum raised against a recombinant form of BP180, this BP/HG autoantibody-reactive region was localized to the epidermal basal lamina immediately adjacent to the hemidesmosome. These findings confirmed the predicted type II transmembrane orientation of the BP180 Ag. Thus, the long, C-terminal collagenous domain of this basal keratinocyte protein projects into the basal lamina and may function as a site of interaction with an extracellular matrix component. It is proposed that autoantibodies directed against the well-defined antigenic site on the BP180 ectodomain may play an initiatory role in subepidermal blister formation in BP and HG patients.
    The Journal of Immunology 12/1993; 151(10):5742-50. DOI:10.1016/0923-1811(93)90940-Q · 5.36 Impact Factor
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    ABSTRACT: Autoantibodies from a patient suffering from endemic pemphigus foliaceus (EPF), a blistering skin disease, were used to screen a lambda gt11 human keratinocyte cDNA library. One immunoreactive cDNA clone (lambda EPF5) containing a 900-base pair insert was isolated and subjected to further analysis. Eight of 25 EPF sera were shown to react with the EPF5 fusion protein on immunoblots. The EPF5 cDNA insert hybridized with a 1.2-kilobase epidermal RNA transcript on a Northern blot. Sequence analysis revealed that lambda EPF5 contained the complete coding sequence for a 24-kDa polypeptide exhibiting significant sequence homology with a family of enzymes known as ubiquitin carrier proteins, or E2s, which are an essential component of the ubiquitin-protein conjugation system. The homology was particularly high in the core region containing the active site cysteine. The keratinocyte ubiquitin carrier protein expressed in bacteria, and isolated either intact or as a glutathione S-transferase fusion protein, exhibited the ability to form a thiol ester linkage with ubiquitin in a ubiquitin activating enzyme (E1)-dependent manner, a characteristic property of ubiquitin carrier proteins. The E2 enzyme encoded by clone EPF5 is the first member of this protein family to be cloned from an epidermal source. Interestingly, the EPF autoantibody-reactive epitope and the ubiquitin carrier protein were shown to be encoded in two different translational reading frames. The relevance of the cloned EPF epitope in the pathogenesis of this autoimmune disorder remains to be determined.
    Journal of Biological Chemistry 09/1992; 267(22):15829-35. · 4.60 Impact Factor