Anti-La positive, anti-Ro negative subset of primary Sjögren's syndrome: anti-La is a reality but is the disease?

Objectives: To characterise the serological and clinical findings in primary Sjögren's syndrome in which anti-La was found without anti-Ro. We hypothesised that a significant portion of these are falsely negative for anti-Ro60.

Methods: Twenty-nine sera from primary Sjögren's syndrome patients were tested for antibodies directed against La and Ro. Anti-La was detected using bovine La treated with or without DNAase and RNAase to identify potential false positivity. Anti-Ro60 antibodies were detected using HEp-2000 substrate (in which cells are transfected with human Ro60) and HEp-2 substrate. Anti-Ro60 and Ro-52 were also tested by in vitro transcription/translation followed by immunoprecipitation assay.

Results: All 29 sera bound La, even after treatment with DNAase and RNAase. Of the 29 sera, 25 were unequivocally negative on HEp-2000 (1:40 dilution). Four samples were anti-Ro60 positive with a speckled pattern, three of the four at 1:320 dilution. Thus, false negative anti-Ro60 exists in a small fraction (14%) of the Ro-negative/La-positive primary Sjögren's patients. However, all the samples were negative for Ro60 and Ro52 by in vitro immunoprecipitation assay. Clinically these patients tended not to have salivary gland pathology characteristic of Sjögren's syndrome.

Conclusions: We found only a small fraction of Ro negative/La positive sera to show positive HEp-2000 pattern. These subjects did not have characteristic findings on pathological examination of minor salivary glands, suggesting these subjects have a process distinct from Sjögren's syndrome.