Inhibition of Rho A activity causes pemphigus skin blistering

The autoimmune blistering skin diseases pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are mainly caused by autoantibodies against desmosomal cadherins. In this study, we provide evidence that PV–immunoglobulin G (IgG) and PF-IgG induce skin blistering by interference with Rho A signaling. In vitro, pemphigus IgG caused typical hallmarks of pemphigus pathogenesis such as epidermal blistering in human skin, cell dissociation, and loss of desmoglein 1 (Dsg 1)–mediated binding probed by laser tweezers. These changes were accompanied by interference with Rho A activation and reduction of Rho A activity. Pemphigus IgG–triggered keratinocyte dissociation and Rho A inactivation were p38 mitogen-activated protein kinase dependent. Specific activation of Rho A by cytotoxic necrotizing factor-y abolished all pemphigus-triggered effects, including keratin retraction and release of Dsg 3 from the cytoskeleton. These data demonstrate that Rho A is involved in the regulation of desmosomal adhesion, at least in part by maintaining the cytoskeletal anchorage of desmosomal proteins. This may open the possibility of pemphigus treatment with the epidermal application of Rho A agonists

Macrophage Migration Inhibitory Factor (MIF) Drives Murine Psoriasiform Dermatitis

The immunomodulator Macrophage Migration Inhibitory Factor (MIF) exerts pleiotropic immunomodulatory activities and has been implicated in the pathogenesis of diverse inflammatory diseases. Expression levels of MIF are also significantly elevated in the skin and serum of psoriasis patients, but the pathogenic significance of MIF in psoriasis is unknown. We have therefore addressed the role of MIF in two mouse models of psoriasis, namely in the imiquimod-induced psoriasiform dermatitis (IIPD) and the IL-23-induced dermatitis model. Daily treatment with Aldara™ cream, containing imiquimod, markedly increased the abundance of MIF in the skin and generated a cellular skin expression pattern of MIF closely resembling that in human plaque psoriasis. Deficiency in MIF significantly alleviated IIPD. On the clinical level, all hallmarks of psoriasiform dermatitis, including erythema, skin infiltration, and desquamation were reduced in Mif−/− mice. On the histopathological level, MIF deficiency decreased keratinocyte hyperproliferation, inflammatory cell infiltration, specifically with respect to monocyte-derived cells, and dermal angiogenesis, suggesting that MIF may be involved in the pathogenesis of psoriasiform dermatitis through several mechanisms. Similarly, MIF deficiency also significantly reduced disease in the IL-23-induced dermatitis model, suggesting that MIF is involved in the pathogenic pathways activated by IL-23 and required to achieve full-blown psoriasiform dermatitis. Collectively, our results lend support to a possible disease-promoting role of MIF in psoriasis, which should be further investigated

Tight Clustering of Extracellular BP180 Epitopes Recognized by Bullous Pemphigoid Autoantibodies

Bullous pemphigoid is a blistering skin disease associated with autoantibodies against the BP180 antigen, a transmembrane component of the hemidesmosome. Anti-BP180 antibodies have been demonstrated to be pathogenic in a passive transfer mouse model. One extracellular site on human BP180 (MCW-1) was previously shown to be recognized by 50–60% of bullous pemphigoid sera. To facilitate the identification of additional autoantibody-reactive epitopes, recombinant forms of the BP180 ectodomain were generated using both bacterial and mammalian expression systems. One recombinant protein, sec180e, that was expressed in COS-1 cells and that contained the entire BP180 ectodomain, provided us with a tool to detect conformational epitopes. Bullous pemphigoid sera immuno-adsorbed against the major noncollagenous NC16A domain no longer reacted with sec180e, indicating that autoantibody reactivity to the BP180 ectodomain is restricted to the NC16A region. Immunoblot analysis of bullous pemphigoid sera immunoadsorbed with a series of recombinant NC16A peptides revealed the presence of three novel autoantigenic sites that, along with the MCW-1 epitope, are clustered within the N-terminal 45 amino acid stretch of NC16A. All 15 bullous pemphigoid sera tested reacted with a recombinant protein containing this BP180 segment. No disease-associated epitopes were detectable within the remaining 28 amino acids of NC16A. Thus, bullous pemphigoid patient autoantibodies react with a set of epitopes on the BP180 ectodomain that are highly clustered. This autoantibody-reactive region on human BP180 shows overlap with the corresponding murine BP180 site that is targeted by antibodies that are pathogenic in the mouse model of bullous pemphigoid. These findings suggest new directions for the development of diagnostic and therapeutic tools for this disease

Identification of Quantitative Trait Loci in Experimental Epidermolysis Bullosa Acquisita

Epidermolysis bullosa acquisita (EBA) is a chronic mucocutaneous autoimmune skin blistering disease. Several lines of evidence underscore the contribution of autoantibodies against type VII collagen (COL7) to the pathogenesis of EBA. Furthermore, EBA susceptibility is associated with the MHC haplotype in patients (HLA-DR2) and in immunization-induced EBA in mice (H2s). The latter study indicated an additional contribution of non-MHC genes to disease susceptibility. To identify non-MHC genes controlling EBA susceptibility, we intercrossed EBA-susceptible MRL/MpJ with EBA-resistant NZM2410/J and BXD2/TyJ as well as Cast mice. Mice of the fourth generation of this four-way autoimmune-prone advanced intercross line were immunized with a fragment of murine COL7 to induce EBA. Anti-COL7 autoantibodies were detected in 84% of mice, whereas deposition of complement at the dermal–epidermal junction (DEJ) was observed in 50% of the animals; 33% of immunized mice presented with overt clinical EBA. Onset of clinical disease was associated with several quantitative trait loci (QTLs) located on chromosomes 9, 12, 14, and 19, whereas maximum disease severity was linked to QTLs on chromosomes 1, 15, and 19. This more detailed insight into the pathogenesis of EBA may eventually lead to new treatment strategies for EBA and other autoantibody-mediated diseases

Epidermolysis Bullosa Simplex Associated with Severe Mucous Membrane Involvement and Novel Mutations in the Plectin Gene

We report a novel case of epidermolysis bullosa simplex with severe mucous membrane involvement and mutations in the plectin gene (PLEC1). The patient suffered from extensive blistering of the skin and oral and laryngeal mucous membranes. Electron microscopy of a lesional skin biopsy showed cleft formation within the basal cell layer of the epidermis. Antigen mapping displayed entirely negative staining for plectin, a large (>500 kDa) multifunctional adhesion protein present in hemidesmosomes of the basal keratinocytes. Mutation analysis revealed compound heterozygous, previously undisclosed nonsense mutations, Q1713X and R2351X, of paternal and maternal origin, respectively, within exon 32 of PLEC1. Based on earlier reports, plectin deficiency is associated with late onset muscular dystrophy in patients with epidermolysis bullosa. No signs of muscle weakness have been observed during the 4 y follow-up of our patient. This case illustrates the fact that molecular pathological analyses have prognostic implications in identification and evaluation of patients who appear to be at risk for development of muscular dystrophy later in life

Dimethylfumarate Impairs Neutrophil Functions

Host defense against pathogens relies on neutrophil activation. Inadequate neutrophil activation is often associated with chronic inflammatory diseases. Neutrophils also constitute a significant portion of infiltrating cells in chronic inflammatory diseases, for example, psoriasis and multiple sclerosis. Fumarates improve the latter diseases, which so far has been attributed to the effects on lymphocytes and dendritic cells. Here, we focused on the effects of dimethylfumarate (DMF) on neutrophils. In vitro, DMF inhibited neutrophil activation, including changes in surface marker expression, reactive oxygen species production, formation of neutrophil extracellular traps, and migration. Phagocytic ability and autoantibody-induced, neutrophil-dependent tissue injury ex vivo was also impaired by DMF. Regarding the mode of action, DMF modulates—in a stimulus-dependent manner-neutrophil activation using the phosphoinositide 3-kinase/Akt-p38 mitogen-activated protein kinase and extracellular signal-regulated kinase 1/2 pathways. For in vivo validation, mouse models of epidermolysis bullosa acquisita, an organ-specific autoimmune disease caused by autoantibodies to type VII collagen, were employed. In the presence of DMF, blistering induced by injection of anti-type VII collagen antibodies into mice was significantly impaired. DMF treatment of mice with clinically already-manifested epidermolysis bullosa acquisita led to disease improvement. Collectively, we demonstrate a profound inhibitory activity of DMF on neutrophil functions. These findings encourage wider use of DMF in patients with neutrophil-mediated diseases