Determination of antibodies to specific nuclear antigens, termed extractable nuclear antigen (ENA), was investigated in healthy dogs and in dogs with autoimmune, inflammatory, and neoplastic diseases. Using a counter-immunoelectrophoresis method, the dogs' sera were tested for antibodies against the nuclear antigens single-stranded DNA, Sm, Ro, La, ribonucleoprotein, Scl, and proliferating cell nuclear antigen. Antibodies to the Ro antigen were found in 1 dog with discoid lupus erythematosus, in 1 dog with pemphigus erythematosus, and in 1 dog with facial pyoderma and chronic superficial keratitis. In 15 dogs, antibodies were detected to ENA, but the precipitin lines were too weak to identify the specific ENA. These antibodies were found in some dogs with systemic lupus erythematosus, discoid lupus erythematosus, pemphigus erythematosus, dermatomyositis, vitiligo, lymphoma; in the dog with facial pyoderma and chronic superficial keratitis; and in 1 healthy dog. The highest percentage of dogs with antibodies to ENA in a large series (> 8) of this study was in dogs with systemic lupus erythematosus (4 of 13; 31%).

Oral keratinocytes from dogs were cultured on either collagen gels or artificial matrices at the air-liquid interface, and the expression of keratinocyte antigens and basement membrane components was determined, using various monoclonal and polyclonal antibodies. Keratinocytes grown on collagen gels expressed pemphigus vulgaris, pemphigus foliaceous, and bullous pemphigoid antigens. Diffuse, suprabasal, and superficial keratinocyte membrane differentiation antigens identified by various monoclonal antibodies also were expressed in a pattern identical to that observed in the native tissue. Laminin and type-IV collagen were deposited at the keratinocyte-collagen interface in a patchy distribution. When synthetic matrices were used, the oral keratinocytes differentiated, but to a lesser extent than cells grown on collagen gels. Antigen expression for cells grown on synthetic matrices was similar to that for cells on collagen, except for failure of the keratinocytes on synthetic membranes to express superficial cell antigens and pemphigus foliaceous antigens.

Pemphigus antigens were localized, by use of immunoelectron microscopy, on canine keratinocytes in vivo on esophageal mucosa and in vitro on established cultured keratinocytes. Convalescent sera from a human being with pemphigus vulgaris and a human being with pemphigus foliaceus reacted with the interdesmosomal cytoplasmic keratinocyte membrane of canine esophagus. Cultured canine keratinocytes expressed the pemphigus vulgaris antigen in a similar pattern, but did not carry the pemphigus foliaceus antigen. The differential presence of cell surface antigens and its relation to various forms of the disease are discussed.