Autoantibodies against Cytochrome P450 Side-Chain Cleavage Enzyme in Dogs (Canis lupus familiaris) Affected with Hypoadrenocorticism (Addison’s Disease)

Abstract

Canine hypoadrenocorticism likely arises from immune-mediated destruction of adrenocortical tissue, leading to glucocorticoid and mineralocorticoid deficiency. In humans with autoimmune Addison’s disease (AAD) or autoimmune polyendocrine syndrome (APS), circulating autoantibodies have been demonstrated against enzymes associated with adrenal steroid synthesis. The current study investigates autoantibodies against steroid synthesis enzymes in dogs with spontaneous hypoadrenocorticism. Coding regions of canine CYP21A2 (21-hydroxylase; 21-OH), CYP17A1 (17-hydroxylase; 17-OH), CYP11A1 (P450 side-chain cleavage enzyme; P450scc) and HSD3B2 (3β hydroxysteroid dehydrogenase; 3βHSD) were amplified, cloned and expressed as 35S-methionine radiolabelled recombinant protein. In a pilot study, serum samples from 20 dogs with hypoadrenocorticism and four unaffected control dogs were screened by radio-immunoprecipitation assay. There was no evidence of reactivity against 21-OH, 17-OH or 3βHSD, but five dogs with hypoadrenocorticism showed immunoreactivity to P450scc compared with controls. Serum samples were subsequently obtained from 213 dogs diagnosed with hypoadrenocorticism and 110 dogs from a hospital control population. Thirty control dogs were randomly selected to establish a threshold for antibody positivity (mean + 3 × standard deviation). Dogs with hypoadrenocorticism were more likely to be P450scc autoantibody positive than hospital controls (24% vs. 1.2%, respectively; p = 0.0016). Sex was significantly associated with the presence of P450scc autoantibodies in the case population, with 30% of females testing positive compared with 17% of males (p = 0.037). Significant associations with breed (p = 0.015) and DLA-type (DQA1*006:01 allele; p = 0.017) were also found. This cross-sectional study indicates that P450scc autoantibodies are present in a proportion of dogs affected with hypoadrenocorticism.

Polymorphisms in the CTLA4 promoter sequence are associated with canine hypoadrenocorticism

“…The pathology in the adrenal gland is consistent with an autoimmune aetiology, characterised, at least in the early stages, by immune cell infiltration, similar to that seen in hAAD [2,4]. Furthermore, circulating autoantibodies, which can be long lived, have been demonstrated in a subset of dogs, and are linked to a susceptibility genotype [5,6].…”

“…In dogs, genetic susceptibility to hypoadrenocorticism has been evidenced through breed predispositions and further revealed by pedigree analyses [21][22][23][24][25][26]. More focussed dissection of underlying genetic factors has shown dog leukocyte antigen (DLA) class II variation to be significantly associated with hypoadrenocorticism [5,[27][28][29]. Whilst the significance of these findings have been contested [30,31] it is the case that fine mapping techniques have confirmed MHC associations in human studies as well as revealing further associations and the importance of epistasis [32].…”

A retrospective study of dogs with atypical hypoadrenocorticism: a diagnostic cut‐off or continuum?

“…While adrenal antibody concentrations are used in the diagnosis of hypoadrenocor-ticism in human patients, they have not been well researched in dogs, and it is unknown if they would have a sufficient sensitivity and specificity to improve clinical diagnosis in dogs. Auto-antibodies against steroid synthesis enzymes have recently been evaluated in dogs (Boag et al 2015). Dogs with hypoadrenocorticism were more likely to have P450 auto-antibodies than controls, but this test may have low sensitivity because only 24% of dogs with hypoadrenocorticism were positive for the auto-antibodies.…”

Evaluation of the genetic basis of primary hypoadrenocorticism in Standard Poodles using SNP array genotyping and whole-genome sequencing

“…Primary hypoadrenocorticism, or Addison’s disease (AD), is an immune-mediated disorder caused by an aberrant T cell response against the outer layers of the adrenal cortex (Hadlow 1953; Schaer et al 1986; Mitchell and Pearce 2012; Frank et al 2013; Boag et al 2015; Cartwright et al 2016). The disease is naturally occurring in both humans and dogs.…”