Characterization of intraepidermal IgG deposits in patients with primary Sjögren's syndrome

In order to characterize the pathomechanisms behind intraepidermal in vivo deposits of IgG, which are found in 68% of patients with primary Sjögren's syndrome (primary SS), skin biopsies and serum from patients with epidermal IgG deposits were examined and compared to normal controls. Double-labelling experiments on skin biopsies, from 5 patients and 5 normal controls, showed that IgG deposits were predominantly located to surface membranes of OKT6 positive Langerhans cells. Only IgG1 and IgG3 were found deposited. Neither IgG2, IgG4, IgM, IgA, IgE, IgD, C1q, C3c, fibrinogen, albumin, beta-2 microglobulin nor C-reactive protein were found deposited in the epidermis of patients. Sera from 6 other patients with primary SS were examined for in vitro and in vivo binding of IgG to normal human epidermis. Using the athymic nude mouse/human skin model we were able to show that serum IgG from patients can be experimentally deposited in vivo in human skin transplants, but in vitro binding could not be demonstrated. The Fc-fragments of epidermal IgG were accessible to binding of anti-Fc-fragment antibodies and protein-A. We suggest that IgG-containing immune complexes constitute the intraepidermal IgG deposits seen in patients with primary SS, and that the binding possible is mediated by Fc-receptors of Langerhans cells and keratinocytes.