Detection of circulating anti-keratinocyte autoantibodies in feline pemphigus foliaceus.

Background: Circulating anti-keratinocyte immunoglobulin (Ig)G targeting desmosomal proteins have been identified in people and dogs with pemphigus foliaceus (PF). By contrast, detection attempts in PF-affected cats have been largely unsuccessful.

Hypothesis/objectives: To detect circulating anti-keratinocyte autoantibodies in PF-affected cats and determine their titres and tissue-staining patterns.

Animals: Thirty PF-affected cats were compared to 11 specific-pathogen free, 15 healthy and 31 allergic cats.

Methods And Materials: Sera were tested by indirect immunofluorescence on canine footpad and buccal mucosal substrates.

Results: Circulating, anti-keratinocyte IgG with a suprabasilar, web-like (intercellular) pattern were detected in the majority of PF-affected cats (23 of 30, 77%), some allergic cats (six of 31, 19%) and one healthy cat (7%). Both footpad epidermis and buccal mucosa were positive in the majority of seropositive PF-affected cats (21 of 23, 91%), and in only one of six (17%) seropositive allergic cats. Staining was limited to the footpad in the remaining seropositive PF-affected and allergic cats and one seropositive healthy cat. Reciprocal IgG titres were significantly higher in PF-affected cats compared to controls (Dunn's post-test, P < 0.0001). Anti-keratinocyte IgM, IgA or IgE were not detected in any sera.

Conclusions And Clinical Importance: These results confirm the presence of circulating anti-keratinocyte IgG in a majority of PF-affected cats and in a small percentage of healthy and allergic cats. Although the molecular target and pathogenic nature of the antibodies remains unknown, the detection of positive immunostaining on buccal mucosal tissue, in addition to the footpad, suggests that the major target antigen of feline PF differs from that reported in dogs.