The Spectrum of Autoimmune Bullous Diseases

Autoimmune bullous diseases are a group of cutaneous disorders characterised by skin blistering or erosions as a result of development of autoimmunity. It can be classified according to the anatomical sites of blister into two types: intraepithelial and subepidermal. It can be subdivided further according to the clinical features, type and location of immunoreactants found on skin biopsy (Table 1 and 2). The term "pemphigus" refers to intraepithelial blistering skin diseases. The term "pemphigoid" refers to blistering diseases occurring at the dermo-epidermal junction in general, although not every subepidermal bullous disease bears the term "pemphigoid" in the nomenclature (Table 2). With extensive research, most of the target antigens of these disorders have been characterised. It is amazing to see that earlier disease classification by clinical features and pathological findings alone did have a molecular basis, as distinct antigens are targets for different entities in most of the subgroup of autoimmune bullous diseases. The antigens of pemphigus are found in desmosomes between keratinocytes, which are organelles mediating intercellular adhesion together with tissue morphogenesis and differentiation. On the other hand, the antigens of subepidermal bullous diseases are found in the basement membrane zone at the dermoepidermal junction. Research in these target antigens has led to a better understanding of their biologic functions, advance in disease diagnosis, monitoring of disease activity, and can be potentially employed for antigen specific therapy. Epidemiology of Autoimmune Bullous Diseases in Hong Kong