Immunopathogenesis of Bullous Pemphigoid

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DESCRIPTION (provided by applicant): Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease characterized by autoantibodies and an inflammatory infiltrate at the lesional site. BP autoantibodies recognize two hemidesmosomal proteins, BP180 and BP230. In vitro and in vivo studies have demonstrated that anti-BP180 IgG autoantibodies fix complement and are pathogenic. NC16A, an extracellular domain of BP180, is the primary target of pathogenic autoantibodies. Elevated proinflammatory cytokines including TNF-α and IL-1ß are present in blister fluids and sera of BP patients. However, the roles of these critical inflammatory mediators and how they are up-regulated in BP remain unknown. Lack of a suitable in vivo system is a major obstacle for studies of inflammatory immune responses in BP using patient-derived autoantibodies. Our lab recently generated a humanized BP180 mouse strain (termed NC16A mice), in which the mouse BP180NC14A domain is replaced by the human BP180NC16A domain. The NC16A mice injected with anti-NC16A autoantibodies develop skin lesions that recapitulate key immunohistological features of BP. Our preliminary results showed that subepidermal blister formation induced by pathogenic antibodies is associated with and dependent on increased levels of TNF-α and IL-1ß, and blocking inflammasome assembly/activation genetically or pharmacologically significantly reduces the IL-1ß level and abolishes subsequent blistering. Therefore, the objective of this proposal is to study the role of inflammasomes in BP using our NC16A mouse model. Our central hypothesis for this proposal is that inflammasomes play a critical role in the development of experimental BP by mediating IL-1ß generation and subsequent inflammatory cell infiltration and tissue injury. To determine whether inflammasomes are involved in experimental BP and to uncover the precise functions of inflammasomes during the subepidermal blistering formation, we propose the following Specific Aims: Aim 1 is to determine whether inflammasome activation is required for experimental BP in NC16A mice; Aim 2 is to determine whether anti-NC16A autoantibody-mediated inflammasome activation takes place in mast cells; Aim 3 will determine whether inflammasome-independent activation of IL-1ß is up-regulated and involved in BP blistering in NC16A mice. The proposed studies seek to establish a direct link between the inflammasome activation and BP, a role which has not been established in BP and any other autoimmune, especially autoantibody-mediated diseases. Since this proposal integrates both disease mechanism studies and preclinical trials, the findings are expected to have a significant impact on the treatment of patients with BP.