[Anti-keratin filament autoantibodies]

IgG anti-keratin-filament autoantibodies occur in all human sera and reach high titres in the sera of patients with various cutaneous and non-cutaneous diseases. At indirect immunofluorescence, these autoantibodies may, depending on their titre, appear as 'upper-cytoplasmic' antibodies or 'stratum-corneum' antibodies. In vitro, IgG anti-keratin-filament autoantibodies significantly enhance (as opsonins) the phagocytosis of keratin-filament aggregates by human monocytes and polymorphonuclear leucocytes. They may therefore, also in vivo, play a role in the removal of insoluble extracellular keratin-filament aggregates generated by necrotic or apoptotic cell death. Keratin (Civatte) bodies and deposits of localized cutaneous amyloid are examples of such keratin-filament aggregates that are found in various skin diseases but are also regularly present in large amounts in normal human skin. IgM anti-keratin-filament autoantibodies, which may, at indirect immunofluorescence, appear as 'general cytoplasmic' antibodies, also occur in all human sera and reach high titres in the sera of patients with various diseases. The regular presence of IgM in keratin bodies or deposits of localized cutaneous amyloid therefore probably represents the binding of IgM anti-keratin-filament autoantibodies to their respective antigens. To what extent these in vivo-bound autoantibodies prevent any further damaging reaction by the immune system in response to the liberation of keratin-filament autoantigen is as yet unclear.