B-cell populations and sub-populations in Sjögren's syndrome

Sjögren's Syndrome (SS) is a chronic inflammatory disorder affecting exocrine glands, in particular the lacrimal and salivary glands. The disease can be primary (pSS) or secondary to other systemic autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus and others. The systemic autoimmune character of pSS is also apparent from the occurrence of (non-organ specific) autoantibodies in this disease. Histopathologically, glandular involvement is characterized by focal accumulation of lymphocytes, particularly around epithelial ducts, with, sometimes, germinal center-like structures. The infiltrates largely consist of T-cells, with a preponderance of CD4-positive T-cells. As a result, the pathology in SS was primarily attributed to T cells. However, a break with the fixation on the role of T cells in pSS came when therapeutic B-cell depletion strategies proved remarkably efficacious in this disease, thereby indicating a major role for B-cells in the immunopathogenesis of pSS. In this regard, a closer look at the composition of B-cells and B-cell sub-populations, both in the peripheral blood and in target tissues, is worthwhile. In this review, we discuss current data on B-cells in pSS. B-cell depletion offers a unique possibility to study the recurrence of (pathogenic) B-cells and their characteristics in pSS patients treated with rituximab. Data on B-cell sub-populations in the peripheral blood and B-cell repertoire in the target tissues following rituximab treatment are discussed as well. We also address their state of activation, repertoire, and relation to B-cell activating factor (BAFF).