Single-cell RNA sequencing of peripheral blood defines two immunological subtypes of Sjögren's disease distinguished by anti-SSA antibodies and aberrant B cell populations.

OBJECTIVES: Sjögren's disease (SjD) is a heterogeneous autoimmune disorder characterized by substantial clinical and molecular diversity. This heterogeneity raises key questions regarding the existence of distinct pathogenic mechanisms underlying disease subtypes. The objective of this study was to comprehensively characterize peripheral immune cell states associated with SjD and to identify features that could enable better patient stratification for targeted treatments. METHODS: We performed single-cell RNA sequencing with surface protein profiling on 1.5 million peripheral blood mononuclear cells (PBMCs) from 333 participants. Individuals were stratified by SjD diagnosis and anti-SSA status to enable comparative analyses between disease subgroups and controls. RESULTS: Our analysis identified two immunological endotypes of SjD, with SSA-positive participants exhibiting a dominant and persistent IFN-I signature that was also associated with altered immune cell composition. Transitional B cells were particularly affected, displaying altered developmental states, reduced BCR diversity, shorter CDR3 regions, and increased predicted interactions with activated immune cell populations, findings consistent with perturbations of early B-cell selection processes. By contrast, SSA-negative SjD participants exhibited limited transcriptional differences compared with symptomatic non-SjD controls, highlighting substantial biological heterogeneity within SjD. CONCLUSIONS: These findings support a two-disease model of SjD and highlight transitional B cells as both a key biomarker and a therapeutic target.