Pemphigus: Etiology, pathogenesis, and inducing or triggering factors: Facts and controversies

Pemphigus includes a group of autoimmune bullous diseases with intraepithelial lesions involving the skin and Malpighian mucous membranes. Pemphigus vulgaris (PV), the most frequent and representative form of the group, is a prototypical organ-specific human autoimmune disorder with a poor prognosis in the absence of medical treatment. The pathomechanism of PV hinges on autoantibodies damaging cell-cell cohesion and leading to cell-cell detachment (acantholysis) of the epidermis and Malpighian mucosae (mainly oral mucosa). A controversy exists about which subset of autoantibodies is primarily pathogenic: the desmoglein-reactive antibodies or those directed against the acetylcholine receptors of the keratinocyte membrane. The onset and course of PV depend on a variable interaction between predisposing and inducing factors. Genetic predisposition has a complex polygenic basis, involving multiple genetic loci; however, the genetic background alone ("the soil"), although essential, is not by itself sufficient to initiate the autoimmune mechanism, as proven by the reports of PV in only one of two monozygotic twins and in only two of three siblings with an identical PV-prone haplotype. The intervention of inducing or triggering environmental factors ("the seed") seems to be crucial to set off the disease. The precipitating factors are many and various, most of them directly originating from the environment (eg, drug intake, viral infections, physical agents, contact allergens, diet), others being endogenous (eg, emotional stress, hormonal disorders) but somehow linked with the subject's lifestyle. As to certain drugs, their potential of provoking acantholysis may be implemented by their interfering with the keratinocyte membrane biochemistry (biochemical acantholysis) and/or with the immune balance (immunologic acantholysis). Viral infections, especially the herpetic ones, may trigger the outbreak of PV or simply complicate its clinical course. The precipitating effect might be due to interferons and other cytokines released by the host as a consequence of the viral attack, which overactivate the immune response. Inductions of PV by physical agents (ultraviolet or ionizing radiation, thermal or electrical burns, surgery and cosmetic procedures), contact allergens (in particular, organophosphate pesticides), dietary factors (eg, garlic, leek, onion, black pepper, red chili pepper, red wine, tea), and emotional stress are rare, but well-documented events. The possible intervention of the environment in the outbreak of PV has been overlooked in the past, but nowadays clinicians perceive it more frequently. The assumption that genetic factors alone are not sufficient to cause the outbreak of the disease, inevitably instills the idea that PV may not occur spontaneously, but always results from an interaction between an individual predisposing genetic background and environmental precipitating factors, often concealed or apparently harmless.