Recombinant human cytokines stimulate neutrophil adherence to IgG autoantibody-treated epithelial basement membranes

IgG4 autoantibodies induce dermal-epidermal separation

Bullous pemphigoid (BP) is a sub-epidermal autoimmune blistering disease associated with autoantibodies to the dermal-epidermal junction (DEJ). Patients' autoantibodies induce dermal-epidermal separation when co-incubated with cryosections of human skin and leucocytes from healthy volunteers. IgG autoantibodies trigger complement and/or leucocyte activation resulting in specific pathology in several autoimmune conditions. In these diseases, IgG1 and IgG3 isotypes, but not the IgG4 subclass, are thought to trigger inflammatory pathways resulting in tissue damage. The capacity of IgG4 autoantibodies to mediate tissue damage has not yet been demonstrated. In this study, we isolated IgG1 and IgG4 autoantibodies from bullous pemhigoid patients'serum and analysed their blister-inducing potential in our cryosection assay. As expected, complement-fixing IgG1 autoantibodies induced sub-epidermal splits in this experimental model. Purified IgG4 did not fix complement, but, interestingly, like IgG1, activated leucocytes and induced dermal-epidermal separation. The potential of IgG4 autoantibodies to induce Fc-dependent dermal-epidermal separation was significantly lower compared to IgG1. Our results demonstrate that IgG4 autoantibodies are able to activate leucocytes and point to a hitherto less recognized function of IgG4. Moreover, for the first time, we clearly demonstrate that BP IgG4 autoantibodies have the capacity to induce leucocyte-dependent tissue damage.

Experimental models of epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is an organ-specific autoimmune disease with a well-defined antigen-autoantibody system. Recently, mutually complementary ex vivo and animal models were developed for this disease. The blister formation of EBA can be reproduced by passively transferring antibodies against type VII collagen into mice. In addition, the Fc-dependent interaction of autoantibodies with granulocytes resulting in dermal-epidermal separation can be studied using patient autoantibodies and leukocytes from healthy donors in cryostat sections of normal human skin. Finally, the autoimmune response and the active blistering disease are replicated by immunizing mice with autologous type VII collagen. The results obtained using these experimental systems provided conclusive evidence that EBA is an antibody-mediated autoimmune disease. In addition, these models represent powerful new tools for understanding EBA pathophysiology and will likely offer unique opportunities to investigate the molecular mechanisms of antibody-mediated autoimmune diseases in general. Thus, due to improved disease modelling, EBA emerges as an exquisitely instructive model disease to study fundamental, biologically and clinically crucial aspects of antibody-mediated organ-specific autoimmune diseases that extend well beyond the limits of autoimmunity against type VII collagen. The new mechanistic insights gained from investigating EBA pathogenesis will facilitate the design of immunomodulatory interventions for this and other pathogenetically related organ-specific, antibody-dependent autoimmune diseases.

Detection of elevated levels of IL-4, IL-6, and IL-10 in blister fluid of bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease with autoantibodies directed against antigens associated with hemidesmosomes of basal keratinocytes. In addition to autoantibodies and activated complement, cellular mechanisms are crucial for blister formation in this disease. Mononuclear cells, which are the first cells infiltrating BP lesions, mainly belong to CD3, CD4+ T-helper (Th) cells. Elevated concentrations of IL-2, IFN gamma, TNF beta, and IL-5 have been recently demonstrated in BP blister fluid. In this study, we were interested in levels of other Th-type cytokines, including IL-3, IL-4, IL-6, IL-10, and GM-CSF in blister fluid of BP. Cytokines were determined by ELISA or bioassay. Levels in the blister fluid from ten BP patients were compared with those in serum samples taken at the time of blister puncture and with those in suction blister fluid of ten healthy volunteers. In blister fluid of BP, we found significantly elevated concentrations of IL-4, IL-6, and IL-10 relative to both concurrent serum samples and suction blister fluid from controls. No differences were detected for either IL-3 or GM-CSF. Our results suggest that IL-4, IL-6, and IL-10 are released at the site of blister formation in BP.

Epidermolysis bullosa acquisita induced by GM-CSF: a role for eosinophils in treatment-related toxicity

A patient treated with granulocyte-macrophage colony-stimulating factor (GM-CSF) developed eosinophilia and epidermolysis bullosa acquisita. The bullae were subepidermal, and filled with an inflammatory infiltrate composed predominantly of eosinophils. Immunofluorescence studies disclosed linear deposition of IgG, IgA and C3 at the basement membrane zone and immunoelectron microscopy demonstrated antibody deposition in the lamina densa and sublamina densa region; however, the patient's serum did not contain circulating antibody to basement membrane zone antigens. Staining with monoclonal antibodies revealed dense deposits of both eosinophil peroxidase and eosinophil major basic protein at the dermal-epidermal junction. The eosinophilia and skin lesions resolved upon discontinuation of GM-CSF. This case provides evidence for two hypotheses: (1) GM-CSF induced proliferation and activation of eosinophils may contribute to some of the toxicities of GM-CSF treatment, and (2) activated granulocytes, including eosinophils, may mediate blister formation in epidermolysis bullosa acquisita.

The role of GM-CSF in infection

GM-CSF is a hemopoietic growth factor with substantial effects on the proliferation of neutrophils, eosinophils and monocytes/macrophages. Its physiologic role in infection is still poorly understood. The gene for GM-CSF is constitutively transcribed in cells substantial for antiinfectious response. Various cells are activated and induced by TNF and IL-1 to synthesize GM-CSF. No systemic GM-CSF levels can be detected in patients with infection. It is likely that GM-CSF plays its physiological role in the immediate vicinity of the cells by which it is secreted. GM-CSF functionally activates neutrophils, monocytes/macrophages and eosinophils. It may augment T-cell proliferation and function. GM-CSF is effective in mice infected with Staphylococcus aureus or Salmonella typhimurium. Its effect in infectious disease in man should be explored.