A second biopsy for direct immunofluorescence (DIF) was taken from uninvolved perilesional skin: the results of DIF showed linear deposition of immunoglobulin G (IgG, faint deposits) and complement component 3 (C3, intense deposits) along the basement membrane zone leading to the diagnosis of bullous pemphigoid (Fig. 3). Here, C3 is linked to bullous pemphigoid.