Involvement of membrane attack complex of complement in UV-B-induced acantholysis in pemphigus

The initial acantholytic process induced by irradiation of UV-B on uninvolved skin of patients with pemphigus was immunohistologically studied using monoclonal antibodies that bind to antigenic determinants present in the C5b9 complex. Membrane attack complex of complement-related antigens in suprabasal intercellular sites could be detected after 5 hours of irradiation, at which time there was no acantholysis. At 24 hours, the staining intensity markedly increased and suprabasal clefts with acantholytic epidermal cells could be seen. In contrast, acantholysis did not develop in the absence of membrane attack complex formation at intercellular sites even 24 hours following UV-B irradiation. These findings suggest that UV-B can induce membrane attack complex assembly in the epidermis, which may itself be involved in the process of acantholysis and provide additional evidence for involvement of the complement system in pemphigus.