Affinity immunoblotting studies on the restriction of autoantibodies from endemic pemphigus foliaceus patients.

Endemic pemphigus foliaceus or Fogo Selvagem (FS) is an autoimmune blistering skin disease mediated by autoantibodies directed against components on the surface of subcorneal keratinocytes. All patients have high titers of these autoantibodies in the IgG4 subclass as determined by indirect immunofluorescence on frozen skin sections. In addition, patients may also have autoantibodies in other IgG subclasses, particularly IgG1, but the titers in these subclasses are significantly lower than those found in the IgG4 subclass. We have now found that in addition to isotype preference, autoantibodies from FS patients show clonal restriction as evidenced by oligoclonal banding on isoelectric focusing after probing with extracts from both human and bovine epidermis. Both IgG1 and IgG4 exhibit oligoclonal banding, but the distribution of these bands in the pH gradient differs for these two subclasses. Whereas the IgG4 oligoclonal bands are distributed throughout the IgG4 pH range, IgG1 banding appears to be concentrated in the more basic region of the IgG1 pH range. This finding suggests that the IgG1 autoantibodies have undergone selective somatic mutation by a negatively charged autoantigen. Similar findings have been reported for pathogenic DNA autoantibodies associated with SLE. The wide distribution of IgG4 banding suggests that this response may have followed the IgG1 response and has not undergone selective mutation. Both IgG1 and IgG4 appear to be Ca++ dependent autoantibodies.