Bullous pemphigoid: etiology, pathogenesis, and inducing factors: facts and controversies.

The term pemphigoids includes a group of autoimmune bullous diseases characterized by subepidermal blistering. Bullous pemphigoid (BP) is not only the most common disorder within the pemphigoid group, but also represents the most frequent autoimmune blistering disease in general. The onset and course of BP depend on a variable interaction between predisposing and inducing factors. HLA genes are the most significant genetic predisposition factor to autoimmunity mechanisms. Many studies show an association between HLA-DQβ1*0301 and distinct clinical pemphigoid variants. Imbalance between autoreactive T helper (Th) and T regulatory cells, toll-like receptor activation, and Th17/IL-17 pathway are the three possible autoimmunity triggers underlying BP. The pathomechanism of BP hinges on an autoantibody response toward structural components of the hemidesmosome (BP180 and BP230). The binding of autoantibodies leads to complement activation, recruitment of inflammatory cells, and release of proteolytic enzymes. The inflammatory cascade also may be directly triggered by activation of Th17 cells with no intervention of autoantibodies. The intervention of inducing factors in BP can be identified in no more than 15% of patients. Facilitating factors in genetically predisposed individuals are various (drug intake, physical agents, and viral infections). Drugs may act as triggers by either modifying the immune response or altering the antigenic properties of the epidermal basement membrane. Cases of induction of BP by physical agents (eg, radiation therapy, ultraviolet radiation, thermal or electrical burns, surgical procedures, transplants) are rare, but well-documented events. A contributing role in inducing BP has been suggested for infections, in particular human herpes virus (HHV) infections (cytomegalovirus, Epstein-Barr virus, and HHV-6), but also hepatitis B and C viruses, Helicobacter pylori, and Toxoplasma gondii. Unlike pemphigus, no dietary triggers have been suspected of being involved in the induction of BP. In all patients who have a diagnosis of BP, an environmental agent as a potential cause should always be considered, because the prompt discontinuation of it might result in rapid improvement or even cure of the disease.