Plasminogen activation in bullous pemphigoid immunohistology reveals urokinase type plasminogen activator, its receptor and plasminogen activator inhibitor type-2 in lesional epidermis

SerpinB2 Deficiency Results in a Stratum Corneum Defect and Increased Sensitivity to Topically Applied Inflammatory Agents

SerpinB2 (plasminogen activator inhibitor type 2) is constitutively expressed at high levels by differentiating keratinocytes in mice and humans; however, the physiological function of keratinocyte SerpinB2 remains unclear. Herein, we show that SerpinB2(-/-) mice are more susceptible to contact dermatitis after topical application of dinitrofluorobenzene, and show enhanced inflammatory lesions after topical applications of phorbol ester. Untreated SerpinB2(-/-) mice showed no overt changes in epithelial structure, and we were unable to find evidence for a role for keratinocyte SerpinB2 in regulating immunity, apoptosis, IL-1β production, proteasomal activity, or wound healing. Instead, the phenotype was associated with impaired skin barrier function and a defective stratum corneum, with SerpinB2(-/-) mice showing increased transepidermal water loss, increased overt loss of stratum corneum in inflammatory lesions, and impaired stratum corneum thickening after phorbol ester treatment. Immunoblotting suggested that SerpinB2 (cross-linked into the cornified envelope) is present in the stratum corneum and retains the ability to form covalent inhibitory complexes with urokinase. Data suggest that the function of keratinocyte SerpinB2 is protection of the stratum corneum from proteolysis via inhibition of urokinase, thereby maintaining the integrity and barrier function of the stratum corneum, particularly during times of skin inflammation. Implications for studies involving genetically modified mice treated with topical agents and human dermatological conditions, such as contact dermatitis, are discussed.

Experimental models for the autoimmune and inflammatory blistering disease, Bullous pemphigoid

Bullous pemphigoid (BP) is a subepidermal skin blistering disease characterized immunohistologically by dermal-epidermal junction (DEJ) separation, an inflammatory cell infiltrate in the upper dermis, and autoantibodies targeted toward the hemidesmosomal proteins BP230 and BP180. Development of an IgG passive transfer mouse model of BP that reproduces these key features of human BP has demonstrated that subepidermal blistering is initiated by anti-BP180 antibodies and mediated by complement activation, mast cell degranulation, neutrophil infiltration, and proteinase secretion. This model is not compatible with study of human pathogenic antibodies, as the human and murine antigenic epitopes are not cross-reactive. The development of two novel humanized mouse models for the first time has enabled study of disease mechanisms caused by BP autoantibodies, and presents an ideal in vivo system to test novel therapeutic strategies for disease management.

Bullous pemphigoid: using animal models to study the immunopathology

Bullous pemphigoid was first described by Lever in 1953 as a subepidermal blistering disease. Its immunohistological features include dermal-epidermal junction separation, an inflammatory cell infiltrate in the upper dermis, and basement membrane zone-bound autoantibodies. These autoantibodies show a linear staining at the dermal-epidermal junction, activate complement, and recognize two major hemidesmosomal antigens, BP230 (BPAG1) and BP180 (BPAG2 or type XVII collagen). An IgG passive transfer mouse model of BP was developed by administering rabbit antimurine BP180 antibodies to neonatal mice. This model recapitulates the key features of human bullous pemphigus. Using this in vivo model system, several key cellular and molecular events leading to the bullous pemphigus disease phenotype were identified, including IgG binding, complement activation, mast cell degranulation, and neutrophil infiltration and activation. Proteinases and reactive oxygen species released by neutrophils work together to damage the basement membrane zone, causing dermal-epidermal junction separation. Recent experimental data from human bullous pemphigus studies suggest that human bullous pemphigus and its mouse IgG passive transfer model counterpart may well share not only common immunohistological features but also pathological mechanisms underlying the development of this antibody-mediated disease.

Molecular and functional characterization of the four-transmembrane molecule l6 in epidermal keratinocytes

In normal human epidermal keratinocytes (NHEK) proteolytic detachment from the substrate induces a complex activation cascade including expression of new proteins, morphological alterations, and the onset of migration for epidermal regeneration. By subtractive cloning we have shown that L6, a four-transmembrane protein, is newly expressed after proteolytic keratinocyte detachment. In this study, we have generated a novel anti-L6 antibody (clone HD-pKe#104-1.1) and investigated L6 expression regulation in vitro and in vivo as well as L6 function in keratinocyte migration. Dispase-mediated detachment induced L6 expression in NHEK at the mRNA and protein level. Immunohistology of skin biopsies displayed a strong expression of L6 in follicular epidermis and epidermolytic lesions of autoimmune bullous dermatoses (bullous pemphigoid, pemphigus vulgaris), but not in normal interfollicular epidermis. In contrast to normal keratinocytes, HaCaT cells showed constitutive L6 expression, indicating a constitutively active phenotype. After artificial wounding of confluent HaCaT cultures, anti-L6 antibody strongly impaired cell migration velocity and migratory reepithelization of the defect, indicating L6 involvement in keratinocyte migration. These findings suggest that L6 is an important activation-dependent regulator of keratinocyte function and epidermal tissue regeneration.

Co-localization of urokinase and its receptor on established human umbilical vein endothelial cell

Vascular endothelial cells possess antithrombotic properties, which are determined by the balance between plasminogen activators (PAs) and PA inhibitors (PAls). A cell line, TKM-33, has been established and cloned from human umbilical vein endothelial cells, was previously reported to produce a large amount of urokinase-type PA (u-PA) and small amounts of tissue-type plasminogen activator (t-PA) and PA inhibitor-1 (PAI-1). Moreover, TKM-33 expressed the u-PA receptor (u-PAR) which plays an important role in the localization of fibrinolytic activity on cell surface. In the present study, we investigated the localization of u-PA, t-PA, PAI-1 and u-PAR in TKM-33 by using immunofluorescence staining technique. The endothelial cells were strongly stained with anti-PAI-1, anti-u-PA and anti-u-PAR IgGs, and slightly with anti-t-PA IgG. The double immunofluorescence staining with mouse anti-u-PA IgG and rabbit anti-u-PAR IgG followed by rhodamine-conjugated anti-mouse IgG and FITC-conjugated anti-rabbit IgG showed the co-localization of u-PA and u-PAR on the same section of endothelial cells. Although u-PA antigen also existed in the cytoplasm of endothelial cells, u-PAR antigen did not. The treatment of endothelial cells with phorbol-myristate-acetate (PMA) upregulated the expression of u-PA and u-PAR antigens. In this stimulation, u-PAR antigen was detected not only on the surface of the cells but also in the cytoplasm. Thus, the binding of u-PA to u-PAR was confirmed by double immunofluorescence staining.