Molecular analysis of pathogenic rheumatoid factor repertoires in patients with primary Sjögren’s syndrome

Primary Sjögren’s syndrome (SS) is a common autoimmune disease characterised by lymphocytic infiltration of salivary and lacrimal glands leading to dry eyes and mouth. These patients often suffer from systemic involvement of lungs and kidneys, and their risk of developing lymphoma is much higher than in the general population.
Rheumatoid factors (RFs) are a group of autoantibodies and commonly found in the saliva and serum of patients with primary SS. They are independent predictors of lymphoma in primary SS. Conventional RF detection assays, used for decades in the clinic, are useful for detecting overall antibody activity, but are unable to distinguish the pathogenic clones at a molecular level. In preliminary studies using sophisticated mass spectrometry (MS)-based proteomic technology, we sequenced RFs directly from human serum and showed that pathogenic (disease causing) RF clonotypic peptides were detectable years before the clinical presentation of life-threatening vasculitis in patients with primary SS, indicating that these surrogate peptides may serve as early diagnostic markers in asymptomatic subjects. Furthermore, we pioneered the use of quantitative barcode proteomics to demonstrate expansion of RF clones during disease progression and their disappearance with immunosuppression. We will extend this discovery by directly MS sequencing RFs and determining their so-called variable (V) region molecular signatures. The IgV signatures can then be used in a novel quantitative MS to track and verify pathogenic RF clonotypes following treatment and during the transition from benign autoimmunity to monoclonal cryoglobulinemic vasculitis and lymphoma. These studies will unravel the enigma of serum RFs repertoire in primary SS, and hopefully lead to more relevant predictive and prognostic markers and more rational therapeutic approaches aimed at removing the pathogenic clones.