Pemphigus foliaceus in cats

Autoimmune skin diseases are characterised by reactions of the immune system against ‘self’ antigens. The reaction can be mediated by antibodies or by cells belonging to the immune system (https://pathology.jhu.edu/autoimmune/definitions). In cats, autoimmune skin diseases are considered uncommon to extremely rare, with the exceptions of pemphigus foliaceus (pemphigus foliaceus) and vitiligo. Currently, the existence of some autoimmune skin disease, such as cutaneous lupus erythematosus, is questioned in the feline species. The autoimmune skin diseases reported in cats are summarised in Table 1. Pemphigus foliaceus is the most common autoimmune skin disease, although it represents only 1% of cases seen by veterinary dermatologists (Scott et al, 2013a).

Pemphigus foliaceus is an antibody-mediated autoimmune skin disease. Autoantibodies belonging to the IgG subclass attack and destroy the desmosomes, the special structures connecting one keratinocyte to another. The clinical result of the detachment of keratinocytes in the upper layers of the epidermis is a pustule, which is the primary pemphigus foliaceus lesion in all affected species (Bizikova, 2020). The target autoantigen within the desmosome has been identified in humans as desmoglein-1 and, more recently, in dogs as desmocollin-1, while it has not yet been identified in cats. A recent study showed that circulating anti-keratinocyte IgG antibodies were present in 77% of cats affected by pemphigus foliaceus. The authors postulated that the target autoantigen is likely to be different from the one identified in dogs and humans (Levy et al, 2020).