Immunohistochemical characterization of intraepidermal in vivo IgG deposits in patients with primary Sjögren's syndrome.

68% of patients with primary Sjögren's syndrome have previously been found to have intra-epidermal in vivo IgG deposits in clinically unaffected skin. In this investigation, we examined immunohistologically skin biopsies from 5 patients with primary Sjögren's syndrome and from 5 normal controls in order to characterize further the intra-epidermal IgG deposits. Employing direct immunofluorescence and peroxidase-antiperoxidase (PAP) techniques, IgG was localized to epidermal cell surfaces. Double-labelling immunofluorescence experiments showed IgG to be bound to OKT6-positive Langerhans cells, and to some degree also to keratinocytes. Only IgG1, IgG3 and in one patient IgA were deposited, whereas IgG2, IgG4, IgM, IgD, IgE, C1q, C3c, C3d, C4, beta-2 microglobulin, albumin, fibrinogen and C-reactive protein were not found deposited in the intra-epidermal area. The epidermal IgG deposits were reactive with anti-Fc-fragment antibodies and with staphylococcal protein-A. These results are compatible with, although not definitive proofs of, the hypothesis that the in vivo deposited IgG is found in the form of IgG-containing immune complexes.