Evidence that the IgA in patients with linear IgA disease is qualitatively different from that of patients with dermatitis herpetiformis.

A previous study using immunofluorescent techniques showed J-chain to be present in the uninvolved skin of patients with papillary IgA dermatitis herpetiformis (DH) in a distribution that was coextensive with the IgA. This implied that the IgA was dimeric and of mucosal origin. In this study, fifteen patients with papillary IgA deposits, fifteen with homogeneous-linear (HL) IgA deposits and four patients with granular-linear (GL) IgA deposits were tested for the presence of in vivo bound J-chain. All fifteen patients with papillary IgA deposits and all four with GL IgA deposits had J-chain staining coextensive with the IgA. However, only one of fifteen patients with HL IgA deposits demonstrated in vivo bound J-chain that could not be accounted for by coexisting IgM deposits. These findings indicate that the IgA in patients with HL deposits is qualitatively different from that in patients with papillary and GL IgA deposits and makes the distinction between the two types of linear fluorescence particularly important.