Bullous Pemphigoid

Bullous pemphigoid (BP) is a chronic autoimmune blistering disease that primarily affects older adults, with a peak incidence in individuals over 70 years of age. It is the most common autoimmune blistering disease, occurring more frequently than pemphigus vulgaris. The pathogenesis involves the production of IgG autoantibodies directed against two hemidesmosomal proteins at the dermal-epidermal junction: BP180 (also called type XVII collagen or BPAG2) and BP230 (also called BPAG1). These hemidesmosomes normally function as anchoring structures that attach the basal keratinocytes of the epidermis to the underlying basement membrane zone and dermis, maintaining the structural integrity of the skin. When IgG autoantibodies bind to BP180 and BP230, they activate the complement cascade (particularly C3 and C5a) at the basement membrane zone. This complement activation recruits inflammatory cells, primarily eosinophils and neutrophils, to the dermal-epidermal junction. These inflammatory cells release proteolytic enzymes (matrix metalloproteinases, elastase, and gelatinase) that degrade the structural proteins anchoring the epidermis to the dermis. The result is a subepidermal split -- the epidermis separates from the dermis BELOW the basal cell layer, creating tense, fluid-filled bullae (blisters)....