What Causes Bullous Pemphigoid
Bullous pemphigoid is caused by autoantibodies targeting hemidesmosomal proteins BP180 (type XVII collagen/BPAG2) and BP230 (BPAG1-e), which are essential for dermal-epidermal adhesion 1.
Pathophysiologic Mechanism
The disease develops when the immune system produces IgG autoantibodies against these structural proteins at the basement membrane zone. This autoimmune attack disrupts the connection between the epidermis and dermis, leading to subepidermal blister formation 2, 1. The pathogenesis involves:
- Autoantibody production: IgG antibodies (and sometimes IgA and IgE) bind to BP180 and/or BP230 proteins along the dermoepidermal junction 2
- Immune cell recruitment: Th2 and Th17 cytokines (IL-4, IL-5, IL-13, IL-17, IL-23) recruit eosinophils and neutrophils to the site 3
- Tissue destruction: Matrix metalloproteinase-9 (MMP-9) production causes dermal-epidermal junction separation, while eosinophils and neutrophils infiltrate and form subepidermal bullae 2, 3
- Cell death pathways: Basal cell necrosis occurs via CASP3-dependent apoptosis and RIP3-dependent necroptosis 4
Contributing Factors
While the fundamental cause is autoimmune, several factors contribute to disease development:
Genetic Predisposition
Multiple genomic regions, particularly within the HLA-II region, influence susceptibility. Genetically predisposed individuals carry susceptibility alleles that modulate immune responses 5.
Drug Triggers
More than 50 medications have been associated with triggering bullous pemphigoid, particularly diuretics and psycholeptic drugs (phenothiazines with aliphatic side chains) 2, 6. When evaluating patients, obtain a detailed drug history covering the preceding 1-6 months 2.
Associated Conditions
Neurological and cardiovascular comorbidities show associations with BP, though the mechanistic relationship remains unclear 2.
Environmental Triggers
Recent evidence suggests indoor pollutants and viral infections may serve as inciting triggers in some cases, though this remains an area of active investigation 7.
Clinical Implication
The multifactorial etiology means that genetically susceptible individuals develop BP when exposed to appropriate environmental or pharmacologic triggers 5. In patients presenting with BP who are on multiple medications, always suspect drug-induced disease, as withdrawal of the offending agent often leads to rapid treatment response without relapses 6.