Detection of antinuclear antibodies by the Inno‐Lia ANA update test in canine systemic rheumatic disease

Background: Certain systemic autoimmune diseases in dogs are characterized by high titers of circulating antinuclear antibodies (ANA), which can be demonstrated by indirect immunofluorescence (IIF). In an earlier study of IIF‐ANA–positive dogs, the Ouchterlony double immunodiffusion (DID) test was used to identify specific autoantibodies. The DID test has largely been replaced with line blot tests in human diagnostic settings. Objective: The objective of this study was to investigate whether the line blot assay Inno‐Lia ANA update test is a useful tool in demonstrating ANA specificities in canine patients with previously diagnosed IIF‐ANA–positive rheumatic disorders. Methods: Serum samples from 3 clinically healthy control dogs and 20 canine patients with clinical signs of systemic rheumatic disease and documented positive results for IIF‐ANA and DID tests were included in the study. The Inno‐Lia ANA update assay was performed with an anti‐canine detection antibody. Results: Six serum samples that had DID positivity with anti‐spliceosomal small nuclear ribonucleoproteins (snRNP) reactivity showed reactivity to multiple snRNP proteins in the Inno‐Lia test. Samples from 2 dogs that had other types of DID positivity also had clear SmB reactivity and 1 had weak reactivity to RNP‐70K. The other serum samples, including controls, were negative. Conclusions: Using the Inno‐Lia ANA update test, multiple snRNP specificities were demonstrated in some canine patients with autoimmune rheumatic disorders. Other canine autoantibodies may exist that are not detected by this test. Further studies are necessary to characterize the target antigen(s) of these remaining autoantibodies in canine sera.