Novel shared antibody specificities in anti-Ro/ La antibody negative Sjögren’s Syndrome

INTRODUCTION Sjögren’s syndrome (SS) is a rheumatic autoimmune disease characterized by focal lymphocytic infiltrates in the lacrimal and salivary glands, severe dry mouth and eyes, pain and debilitation. Diagnosis requires autoantibodies to ubiquitous Ro antigens or a lip biopsy positive for focal lymphocytic infiltrates. Here we used human proteome arrays to identify novel antibodies in plasma from Ro positive and Ro/La antibody negative SS patients compared with healthy controls.

METHODS Anti-Ro positive (n=15) and anti-Ro negative (n=15) cases meeting 2016 ACR/EULAR classification criteria for SS were age, race, and sex matched with each other and healthy controls (n=15). Plasma IgG binding to human proteome arrays containing >19,500 recombinant human proteins representing >80% of the human proteome (HuProt v3.2 arrays, CDI Laboratories) was assessed. Data were normalized by the Robust Linear Model using the PAA Bioconductor Package in R and log intensity values for each protein generated. Thresholds of mean + 4SD were established using the controls. Antigens bound by IgG more frequently in cases compared to controls (p<0.05, one-tailed Fisher’s exact test) were considered significant.

RESULTS IgG from Ro positive SS cases significantly bound 18 proteins, including the canonical SS antigens Ro60 and Ro52. IgG from Ro negative SS cases significantly bound 4 proteins compared to controls, 3 of which were shared with the Ro positive group. Binding to any one of 4 novel proteins identified 73% of the Ro negative SS cases.

CONCLUSION A total of 17 novel antigen specificities were identified in SS, with 4 antigens being bound by plasma IgG from Ro/La negative SS cases. These antigens may be useful for diagnosing SS without a lip biopsy.