Pemphigus immunoglobulin G subclass autoantibodies: studies of reactivity with cultured human keratinocytes

The subclass distribution of pemphigus vulgaris (PV) autoantibodies has been investigated further. Cultured human keratinocytes (HuKs) were incubated with immunoglobulin G (IgG) fractions prepared from the serum samples of five patients with PV and one patient with pemphigus foliaceus (PF). The binding of IgG subclasses to HuK was detected by the use of indirect immunofluorescence done with monoclonal antibodies that were specific for each of the four human IgG subclasses. IgG1 and IgG4 binding to keratinocytes was detected in all of the pemphigus IgG preparations. In each instance, the titer of bound IgG1 was equal to or greater than the IgG4 titer. IgG3 binding was detected in only one PV IgG, and IgG2 pemphigus antibody activity was not detected. Differences in the immunofluorescence patterns between the five PV and one PF IgG and between the five PV and a second PF serum were noted. PV antigens were detected as a speckled pattern on HuKs, with accentuation in the intercellular spaces. By comparison, the pattern of PF antigen expression varied significantly depending on whether anti-IgG1 or anti-IgG4 antisera were used. Anti-IgG1 bound in a coarse granular pattern without accentuation in the intercellular spaces, but anti-IgG4 bound in a pattern nearly identical to that observed with PV IgG and its subclasses.