Investigations on the nature and pathogenicity of circulating antikeratinocyte antibodies in dogs with pemphigus foliaceus

Abstract

In humans with pemphigus foliaceus (PF), pathogenic autoantibodies are principally of IgG4 subclass and they cause superficial vesiculation when injected into neonatal mice. The objectives of this study were to determine the isotypes of circulating antikeratinocyte antibodies in dogs with PF, to assess whether serum antikeratinocyte antibody titres decreased during successful treatment, and to study whether such antibodies were pathogenic in passive transfers. Using indirect immunofluorescence with neonatal mouse skin substrates, circulating antikeratinocyte IgG antibodies were detected in 36 of 44 dogs with PF (82%). Serum autoantibodies belonged predominantly to IgG4 (three of 44; 80%) and IgG1 (30 of 44; 68%) subclasses. Antikeratinocyte IgG antibodies were detected in 16 of 20 normal dogs (80%), and these antibodies were IgG1 (16 of 20, 80%) but rarely IgG4 (two of 20; 10%) isotypes. In four dogs, IgG4 antikeratinocyte antibody titres decreased concomitantly to lesions nearing or reaching complete remission. In contrast, IgG or IgG1 titres remained stable or increased when lesions abated. Antikeratinocyte antibodies targeted mainly intercellular autoantigen(s) in the stratum granulosum, while in fewer dogs, such antibodies bound to cytoplasmic basal antigen(s). Intradermal injections of PF or pemphigus vulgaris (PV) IgG into neonatal mice caused subgranular or suprabasal acantholytic vesiculation without granulocyte infiltration, respectively. Similar transfers of normal dog IgG did not cause vesiculation. These observations suggest that antikeratinocyte IgG4 antibodies could be relevant to disease pathogenesis. Importantly, canine PF or PV IgG appear to be pathogenic when transferred passively into mice, causing vesiculation at epidermal levels similar to those of the natural disease.

Metaflumizone–amitraz (Promeris)‐associated pustular acantholytic dermatitis in 22 dogs: evidence suggests contact drug‐triggered pemphigus foliaceus

“…For comparative laboratory investigations, archived skin biopsy‐containing paraffin‐embedded blocks from 10 dogs with spontaneous autoimmune PF (AIPF) were retrieved. These cases were selected because of a clinical phenotype of facial‐predominant, erosive and crusted dermatitis, microscopic demonstration of neutrophil‐rich pustules containing numerous acantholytic keratinocytes and circulating antikeratinocyte IgG autoantibodies as described previously 4 . In these 10 dogs, there had been no history of drug administration compatible with the diagnosis of drug‐associated PF.…”

“…To investigate whether antikeratinocyte antibodies were present in the serum of affected patients, blood was collected from selected cases, whenever possible, and isolated sera were kept frozen until testing at North Carolina State University. Indirect IF was performed, as done routinely in our laboratory, 4 using both normal canine footpad and buccal mucosa as substrates. The titre of IgA antikeratinocyte membrane autoantibodies was determined starting at 1:10, with doubling dilutions until extinction of any positive signal.…”

Expression of keratins, epidermal proteins and inflammatory cells in superficial pemphigus dogs

“…Furthermore, it is important to note that an association between epidermal-specific auto-antibodies and complement proteins has been described previously in human pemphigus (Lessey et al, 2008;Qian et al, 2011); a cross-reaction among IgE, IgM, and IgG4 anti-DSG-1 response has been reported in human PF patients (Qian et al, 2011). In contrast, IgM autoreactivity was not detected when canine PF serum was used against either DSG-1 or DSC-1 (Bizikova et al, 2014), and canine PF showed dominant IgG auto-antibody reactivity (Pérez et al, 2002: Olivry et al, 2009). Moreover, a previous study also detected IgM-producing B-cells in the extracellular matrix of the dermis and in the intercellular epidermis in canine PF (Pérez et al, 2002).…”

“…Therefore, the IgM auto-antibody response may be less predominant than the IgG response or it may correspond to cross-reactivity in individual dogs with pemphigus. Immunostaining for IgG, IgG1 and IgG4 was predominant in the stratum granulosum of PF dogs which probably correlates with disease activity as IgG auto-antibodies have been shown to cause blister formation in the skin of experimental mice by passive transfer of IgG antibodies (Olivry et al, 2009). Similarly, abundant mast cells in the pustules of pruritic skins were observed in feline PF (Preziosi et al, 2003).…”

Fipronil–amitraz–S‐methoprene‐triggered pemphigus foliaceus in 21 dogs: clinical, histological and immunological characteristics

“…Desmoglein‐1 (DSG1), the second critical desmosomal protein in the upper epidermis and the major target autoantigen in human PF, appears to be recognized by only a minority of tested dogs with PF . Although the pathogenic significance of anti‐DSC1 or anti‐DSG1 IgG autoantibodies in canine PF has not yet been demonstrated, the pathogenic nature of the total antikeratinocyte IgG has been documented by passive transfer experiments in neonatal mice …”