B-cell activating factor (BAFF) is a major cytokine that regulates B-cell survival, maturation and differentiation through its binding with its receptors: BAFF receptor (BAFF-R), transmembrane activator and cyclophilin ligand interactor (TACI) and B-cell maturation antigen (BCMA). These receptors have been demonstrated to be involved in tertiary lymphoid structure formation; however, their role in germinal centers (GCs) has remained elusive. The aim of the present study was to determine the expression profiles of BAFF and its receptors in secondary lymphoid tissues. Tonsils resected due to chronic tonsillitis were used as lymphoid tissues. To confirm the presence of GCs identified based on their typical structure, CD21 antibody staining was employed. The expression of BAFF, BAFF-R, TACI and BCMA was assessed by immunohistochemistry. BAFF was highly expressed in all regions of the follicle, but the highest BAFF expression was detected in the mantle zone (MZ). A high expression of BAFF-R was observed on lymphocytes in the MZ in comparison with the other regions (~80%; P<0.05), which was co-localizated with BAFF (r=0.646; P<0.001), in the MZ. TACI and BCMA exhibited similar expression among the different zones of the GCs, and co-localization with BAFF was observed inside the follicle, mainly in the dark zone. The present results indicate that BAFF is implicated in the maintenance of GCs. BAFF-R overexpression in the MZ, co-localizated with BAFF, suggests that these proteins constitute the principal pathway for the maintenance of the naïve B-cell population. Furthermore, TACI and BCMA have a role in the GC, where processes of B-cell selection, proliferation and differentiation into immunoglobulin-secreting plasma cells occur.
Keywords: B-cell activating factor; B-cell activating factor receptor; B-cell maturation antigen; expression; germinal centers; transmembrane activator and cyclophilin ligand interactor.