Role of different pathways of the complement cascade in experimental bullous pemphigoid

Abstract

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease associated with autoantibodies directed against the hemidesmosomal proteins BP180 and BP230 and inflammation. Passive transfer of antibodies to the murine BP180 (mBP180) induces a skin disease that closely resembles human BP. In the present study, we defined the roles of the different complement activation pathways in this model system. Mice deficient in the alternative pathway component factor B (Fb) and injected with pathogenic anti-mBP180 IgG developed delayed and less intense subepidermal blisters. Mice deficient in the classical pathway component complement component 4 (C4) and WT mice pretreated with neutralizing antibody against the first component of the classical pathway, C1q, were resistant to experimental BP. These mice exhibited a significantly reduced level of mast cell degranulation and polymorphonuclear neutrophil (PMN) infiltration in the skin. Intradermal administration of compound 48/80, a mast cell degranulating agent, restored BP disease in C4 -/-mice. Furthermore, C4 -/-mice became susceptible to experimental BP after local injection of PMN chemoattractant IL-8 or local reconstitution with PMNs. These findings provide the first direct evidence to our knowledge that complement activation via the classical and alternative pathways is crucial in subepidermal blister formation in experimental BP. IntroductionBullous pemphigoid (BP) is a subepidermal blistering skin disorder of the elderly (1). Lesional skin of BP patients is characterized by a detachment of the basal keratinocytes of the epidermis from the dermis, resulting in tense, fluid-filled vesicles. Similar skin lesions were noted in herpes gestationis (HG), a nonviral disease of pregnancy (2). Immunofluorescence (IF) studies demonstrated that these patients exhibit circulating and tissue-bound autoantibodies directed against antigens of the basement membrane zone (BMZ) (3-8).BP and HG autoantibodies recognize 2 antigens, BP230 and BP180, that are localized in the hemidesmosome, the main epidermal structure involved in dermal-epidermal adhesion (4-6, 9). The BP230 antigen is restricted to the cytoplasmic plaque of the hemidesmosome and appears to interact directly with the intermediate filament network (10, 11). The BP180 antigen is a type II transmembrane protein with an aminoterminal endodomain and an extended carboxyterminal ectodomain that spans the lamina lucida, projecting into the lamina densa of the BMZ (12-16). The ectodomain of human BP180 contains a series of 15 interrupted collagen domains (complement components 1-15 [C1-C15]) with the typical Gly-X-Y repeat (14). It has recently been shown that the BP180 extracellular domain forms a collagen triple helix (17, 18). The extracellular noncollagenous stretches are designated NC1 (located at the carboxyl terminus) through NC16A (adjacent to the membrane-spanning domain). The NC16A domain of human BP180 harbors major extracellular antigenic sites recognized by BP and HG sera (19,20).Complement can be activated...

Hsp90 blockade modulates bullous pemphigoid IgG-induced IL-8 production by keratinocytes

“…The rationale of our study to probe the effects of 17-DMAG on BP IgG-induced IL-6 and IL-8 production by HaCaT cells was mainly based on three documented findings: (i) both inflammatory cytokines play a key role in the pathophysiology of BP (Schmidt et al 1996a, b;Liu et al 1997;Inaoki and Takehara 1998;Schmidt et al 2000;Chen et al 2001;Schmidt et al 2001;Nelson et al 2006;Messingham et al 2011), (ii) the extensive list of Hsp90 client proteins includes many proinflammatory molecules (Salminen et al 2008;Taipale et al 2010;Henderson and Kaiser 2013), and (iii) recent evidence suggests that Hsp90 represents a novel treatment target in autoimmune bullous diseases (Kasperkiewicz et al 2011;Tukaj et al 2013).…”

“…Although the precise sequence of these events is largely unknown, it has been proposed that one of the first steps leading to blister formation in BP comprise the binding of autoantibodies to BP180, thereby initiating Fc receptor-independent events leading to the release of interleukin 6 (IL-6) and IL-8 from basal keratinocytes (Schmidt et al 2000(Schmidt et al , 2001Messingham et al 2011). IL-8 is a potent chemoattractant for pathophysiologically relevant leukocyte effector cells and together with IL-6 known to be elevated in sera and blister fluids of BP patients and critical for blister formation in mouse models (Schmidt et al 1996a, b;Liu et al 1997;Inaoki and Takehara 1998;Chen et al 2001;Nelson et al 2006;Kobayashi 2008).…”

The C5a Receptor on Mast Cells Is Critical for the Autoimmune Skin-blistering Disease Bullous Pemphigoid

“…Level of Skin C5a-We previously reported that the classical pathway of complement activation is critical to the pathogenesis of experimental BP in mice (18). Wild-type mice (C4 ϩ/ϩ ) and mice deficient in the alternative pathway component factor B (Fb Ϫ/Ϫ ) developed subepidermal blisters following injection with pathogenic anti-murine BP180 IgG; however, mice deficient in the classical pathway component C4 (C4 Ϫ/Ϫ ) were resistant to blister formation ( Fig.…”

“…The complement system and MC activation are indispensable to the pathogenesis of experimental BP (18,40). Having demonstrated that p38 MAPK activation is also required for disease development, we next investigated the links between complement, MCs, and p38 MAPK.…”

“…Using an animal model of BP in which neonatal BALB/c mice are injected with anti-murine BP180 antibodies, we previously demonstrated that dermal-epidermal separation is triggered by anti-BP180 IgG and depends on complement activation, mast cells (MCs), and neutrophils (PMNs) (15)(16)(17). The binding of pathogenic IgG to BP180 activates the classical pathway of the complement and leads to MC degranulation, PMN recruitment, and subsequent skin blistering (18). However, the cellular processes linking complement activation and MC degranulation are not defined in BP.…”