Production of RANKL by Memory B Cells: A Link Between B Cells and Bone Erosion in Rheumatoid Arthritis

Abstract

Objective Rheumatoid arthritis (RA) is a systemic autoimmune disease that often leads to joint damage. The mechanisms of bone damage in RA are complex, involving activation of bone-resorbing osteoclasts (OCs) by synoviocytes and Th17 cells. This study was undertaken to investigate whether B cells play a direct role in osteoclastogenesis through the production of RANKL, the essential cytokine for OC development. Methods RANKL production by total B cells or sorted B cell subpopulations in the peripheral blood and synovial tissue from healthy donors or anti–cyclic citrullinated peptide–positive patients with RA was examined by flow cytometry, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistochemical analysis. To define direct effects on osteoclastogenesis, B cells were cocultured with CD14+ monocytes, and OCs were enumerated by tartrate-resistant acid phosphatase staining. Results Healthy donor peripheral blood B cells were capable of expressing RANKL upon stimulation, with switched memory B cells (CD27+IgD−) having the highest propensity for RANKL production. Notably, switched memory B cells in the peripheral blood from RA patients expressed significantly more RANKL compared to healthy controls. In RA synovial fluid and tissue, memory B cells were enriched and spontaneously expressed RANKL, with some of these cells visualized adjacent to RANK+ OC precursors. Critically, B cells supported OC differentiation in vitro in a RANKL-dependent manner, and the number of OCs was higher in cultures with RA B cells than in those derived from healthy controls. Conclusion These findings reveal the critical importance of B cells in bone homeostasis and their likely contribution to joint destruction in RA.

Generation mechanism of RANKL+ effector memory B cells: relevance to the pathogenesis of rheumatoid arthritis

“…During the preparation of this manuscript, Meednu et al very recently showed that combinatorial stimulation with anti-CD40 and phorbol 12-myristate 13-acetate (PMA) induced RANKL expression in memory B cells and promoted osteoclast differentiation in vitro [36]. These impressive findings emphasize a potential role of effector B cells in osteoclastogenesis involved in RA.…”

“…These impressive findings emphasize a potential role of effector B cells in osteoclastogenesis involved in RA. Here, instead of fixed cells frequently used in the co-culture system [36, 37], we applied the novel system using macrophage RAW264 Venus reporter cells to monitor osteoclastogenesis co-cultured with live B cells, and showed that switched-memory B cells did facilitate osteoclastogenesis (Fig. 4).…”

Synovial Immunophenotype and Anti–Citrullinated Peptide Antibodies in Rheumatoid Arthritis Patients

“…Activation of T cells, particularly those of the proinflammatory Th17 cell subset, fosters the expression of RANKL and also induces osteoclastogenesis (48). Furthermore, previous studies have shown that activated B cells can induce osteoclast differentiation, an effect mediated through increased expression of RANKL on their surface (50,51). Furthermore, previous studies have shown that activated B cells can induce osteoclast differentiation, an effect mediated through increased expression of RANKL on their surface (50,51).…”

Denosumab: targeting the RANKL pathway to treat rheumatoid arthritis

“…Given that elevated serum and tissue RANKL concentration were detected in RA patients (19, 68-71), rheumatoid bone and joint destruction in RA are likely mediated by RANKL-induced OC differentiation (Figure 1). Many cell types, including T lymphocytes, B cells and osteoblasts (OB), release RANKL during the course of RA (72, 73). Several cellular factors including PTH (74) and CXCL16 are involved in the regulation of RANKL (20).…”

“…RANKL-expressing Th17 cells stimulate mature but non-resorptive osteoclasts to resorb bone (87, 88). In addition, RANKL secreted by memory B cells promotes bone erosion in RA (73) and OC formation in an ovariectomy model of osteoporosis (89). Lastly, RANKL was known to induce immune tolerance by promoting the differentiation of Treg cells (90-92).…”