DETECTION OF ANTINUCLEAR ANTIBODIES BY INDIRECT IMMUNOFLUORESCENCE INDOG SERA - COMPARISON OF RAT-LIVER TISSUE AND HUMAN EPITHELIAL-2 CELLS AS ANTIGENIC SUBSTRATE

Rat liver sections and a human epithelial cell line (HEp-2) were compa red as substrates for the detection of antinuclear antibodies (ANA) in the serum of normal dogs and dogs with suspected autoimmune disease, using a standard indirect immunofluorescence (IIF) technique. Antibody reactivity against rat hepatocyte nuclei was frequently found at low serum dilutions in normal dog sera. Using rat liver sections, a minimu m significant positive titer, allowing negativity in more than 95% of normal dog sera, was found to be 1/100. With this titer, ANA positivit y could be verified in 64 of 112 (57%) reanalysed serum samples from d ogs with suspected autoimmune disease, earlier determined as ANA-posit ive, No reactivity against nuclei of HEp-2 cells was observed in any o f the normal dog sera analyzed at a screening dilution of 1/25. Using this dilution as a minimum significant positive titer, 63 of the 112 ( 56%) re-evaluated serum samples were positive. These 63 samples were f rom the same dogs as the 64 samples that were positive on rat liver se ctions. Thus, the 2 methods of ANA-IIF detected a nearly identical pop ulation of dogs with suspected autoimmune disease once the level of si gnificance of a positive titer was adjusted to >95% specificity for ea ch method. HEp-2 cells were found to be superior to rat liver cryostat e sections as ANA substrate because of their low reactivity with norma l sera, and the ease of discernment of the ANA fluorescence pattern, T he recognition and documentation of specific pattern types may give cl ues to ANA subspecificities, which could prove useful if they are foun d to correlate with well-defined subgroups of immune mediated clinical diseases in dogs. Copyright (C) 1996 by the American College of Veter inary Internal Medicine.