2.

IgG4 autoantibodies, in contrast to IgG1, do not fix complement to the dermal–epidermal junction. In a representative experiment, cryosections of normal human skin were incubated with serum and purified antibody preparations from patient 2 and, subsequently, treated with fresh human serum as a source of complement. Both serum (A) and purified IgG1 autoantibodies (B) fixed complement C3 at the dermal–epidermal junction in a linear fashion. In contrast, incubation of cryosections with IgG4 specific for the dermal–epidermal junction (C) or serum from a healthy control (D) does not result in C3 deposition (all magnifications, ×200).