TNFSF11 and rheumatoid arthritis: Since the cytokine RANKL is crucial for the differentiation of mature, multinucleated, bone resorbing osteoclasts from mononucleated progenitor cells (43) and since the RANKL neutralizing antibody Denosumab inhibits bone erosion in arthritic joints without affecting synovial inflammation in RA patients (44, 45) we used antibodies neutralizing mouse RANKL.