Specific forms of BAFF favor BAFF receptor-mediated epithelial cell survival.

Although B cell activating factor (BAFF) and its receptor BR3 are produced and expressed by many cells, their role has been restricted to the lymphocyte lineage. Using various techniques (RT-PCR, indirect immunofluorescence, flow cytometry analysis), we observed the expression of BR3 and the production of BAFF by the human salivary gland cell line, by epithelial cells from biopsies of Sjögren's syndrome patients and their controls, but also by salivary gland epithelial cells in culture. To decipher the role of BAFF and BR3 on epithelial cells, BAFF and BR3 were neutralized by blocking antibodies or RNA specific inhibitor (siBR3) and epithelial cell survival was analyzed. Blocking BR3 promotes epithelial cell apoptosis in vitro. This apoptosis resulted in the nuclear translocation of PKCδ. BAFF neutralization by various anti-BAFF antibodies leads to different effects depending on the antibody used suggesting that only some forms of BAFF are required for epithelial cell survival. Our study demonstrates that BR3 is involved in the survival of cultured epithelial cells due to an autocrine effect of BAFF. It also suggests that epithelial cells produce different forms of BAFF and that only some of them are responsible for this effect.

Epigenetics and Sjögren's syndrome.

There is growing evidence that epigenetics, the study of heritable changes in gene expression that do not involve mutations in the DNA itself, may play an essential role in autoimmune diseases (AID). In Sjögren's syndrome (SS), a chronic AID characterized by an epithelis of the exocrine glands, epigenetic studies have focused on three mechanisms: DNA methylation and its consequences including human endogenous retrovirus (HERV) expression; microRNA expression; and protein post-translational modifications associated with autoantibody production. Although in its infancy, comprehension of the epigenetic (dys)regulation in SS may help us to understand: why SS affects predominantly middle-aged women; why genetically predisposed individuals develop SS but not others; why flare-ups occur; why treatment responses differ between patients; and why some patients develop lymphoma. From these studies will arise a better comprehension of the pathophysiology of SS as well as development of new diagnostic and prognostic biomarkers, and novel therapeutics for prevention and perhaps early intervention.

In Sjögren's syndrome, B lymphocytes induce epithelial cells of salivary glands into apoptosis through protein kinase C delta activation.

Sjögren's syndrome (SS) is a chronic autoimmune epithelitis associated with diffuse lymphocytic infiltration that varies in composition and differs according to lesion severity. T lymphocytes have been viewed as competent in their own right in the destruction of epithelial cells, whereas B lymphocytes that predominate in severe lesions have never been implicated in direct tissue damage. Using co-culture experiments with human salivary gland (HSG) cell line cells and tonsilar B lymphocytes, we observed that direct HSG cell-B lymphocyte contacts were able to induce apoptosis in epithelial cells. This B lymphocyte-mediated cell death could not be ascribed to Fas-Fas ligand interactions but required translocation of protein kinase C delta (PKC δ) into the nucleus of epithelial cells. Ultimately, activation of PKCδ resulted in histone H2B phosphorylation on serine 14 and poly (ADP-ribose) polymerase cleavage. Our results suggest that B lymphocytes infiltrating the SGs of patients with SS could evoke epithelial cell apoptosis.

B-cell tolerance breakdown in Sjögren's syndrome: focus on BAFF.

Sjögren's syndrome (SS) is an autoimmune epithelitis hallmarked by a destruction of epithelial cells, the subsequent lymphocytic infiltration of exocrine glands and their ensuing dryness. Given the prominent role currently assigned to B cells in SS, it is not surprising that the B cell activating factor belonging to the Tumor Necrosis Factor family (BAFF) is involved in its pathogenesis. When overexpressed, this cytokine leads to self-reactive B cells emergence at the transitional B-cell stage. BAFF overexpression that has been observed in SS, is associated with B-cell tolerance breakdown and autoantibody production. Furthermore, BAFF is responsible for the abnormal distribution of B cells subsets and B-cell hyperactivity described in the blood. In the salivary glands, a minority of B-cell clusters represent ectopic germinal center cells, while the majority manifest features consistent with transitional type 2 (T2) and marginal-zone (MZ)-like B cells. Interestingly, both types of B-cell cluster include autoreactive B cells and BAFF is associated with expansion of T2 B cells and MZ-like B cells in the salivary glands. Finally, BAFF plays a major role in B-cell repopulation after their depletion by rituximab in SS.