Canine antinuclear antibodies: comparison of immunofluorescence staining patterns and precipitin reactivity

The occurrence of antinuclear antibodies (ANAs) against several specific nuclear antigens is clearly associated with certain systemic rheumatic disorders in human patients. Determination of ANAs on a routine basis, usually by indirect immunofluorescence (IIF) technique, has therefore become an important diagnostic tool. The subdividing of positive ANA-sera into different nuclear IIF staining patterns often gives clues to antibody specificity. The present investigation aimed at studying whether such subgroups of staining patterns in IIF ANA positive canine sera may represent certain specific ANAs that can be verified by standard methods used for specificity determination in humans. The presence of precipitating antibodies, determined by the Ouchterlony immunodiffusion (ID) technique, was found to be strictly associated with a positive IIF ANA, exhibiting a speckled staining pattern without any chromosomal reactivity. None of the sera with chromosomal reactivity contained precipitating antibodies. Among the ID positive serum samples, different antigenic reactivities were detected, represented by different ID subgroups. Only 1 of the 4 main subgroups obtained by ID showed identity with any of the common and disease-associated human ANA specificities, exhibiting anti-RNP reactivity. One of these serum samples concomitantly exhibited precipitating antibodies against the Sm antigen.