Circulating antinuclear antibodies (ANAs) are commonly present in the systemic autoimmune disease systemic lupus erythematosus (SLE) and in other SLE-related diseases, in humans as well as in dogs. Certain canine breeds, such as German shepherd dogs and Nova Scotia duck tolling retrievers (NSDTRs), have been shown to be overrepresented for autoimmune diseases.

The indirect immunofluorescence (IIF)-ANA test is the standard method for detecting ANAs. Further testing for ANA specificities with different techniques, such as ELISAs, immunoblot or immunodiffusion, is routinely performed in humans, but not in dogs, to aid in the diagnosis of disease. Several specific ANAs identified in humans have been identified also in suspected canine SLE or SLE-related disorders but in many cases the main antigen targeted by the antibodies cannot be identified. IIF-ANA positive dogs are usually divided into two subgroups depending on their fluorescence pattern, a speckled pattern with no chromosomal reactivity or a homogenous pattern with chromosomal reactivity. Previous studies have shown that only dogs with a speckled IIF-ANA pattern are positive on immunodiffusion.

Our aim was to investigate if the immunodiffusion (ID) technique, using sera from IIF-ANA positive dogs, may identify specific ANAs of relevance in human patients and also identify different subgroups of unknown antigens.

Sera from 32 IIF-ANA positive dogs with speckled fluorescence pattern were part of the study (21 German shepherd dogs, three NSDTRs and eight dogs of seven other different breeds). Ten healthy dogs of different breeds were used as controls. Thirty-one of the 32 IIF-ANA positive dogs were positive on immunodiffusion. Twenty-nine of the positive dogs could be further divided into three separate groups based on their reactions on immunodiffusion. Group 1 (n=4) and group 2 (n=16) had reactivity to unknown antigens (different between the groups). Group 3 (n=9) had antibodies directed to RNP. A breed associated ANA specificity was observed in both NSDTRs and German shepherd dogs. All NSDTRs belonged to group 1, while group 2 consisted only of German shepherd dogs.

The ID technique thus shows that IIF-ANA canine sera may be divided into subgroups reflecting the same specific ANA reactivity. In most of the dogs the specific ANA reactivity could not be identified, which might indicate dog-specific autoantigens. Further investigations of canine sera are needed in order to identify the specific antigen reactivity of these ANAs.

Disclosures

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