Dual effect of IL-7/IL-7R signalling on the osteoimmunological system: a potential therapeutic target for rheumatoid arthritis.

The IL-7/IL-7R pathway plays a vital role in the immune system, especially in the inflammatory response. Monocytes/macrophages (osteoclast precursors) have been recently recognized as important participants in the osteoclastogenesis of rheumatoid arthritis (RA) patients. Here, we aimed to investigate the therapeutic potential of IL-7/IL-7R pathway in RA and to determine whether it could restrain osteoclastogenic functions and therefore ameliorate RA. Firstly, collagen-induced arthritis (CIA) mice were administered with IL-7Rα-target antibodies to assess their therapeutic effect on arthritis. We found that blockade of the IL-7/IL-7R pathway protected CIA mice from bone destruction in addition to inducing inflammatory remission, by altering the RANKL/RANK/OPG ratio and consequently decreasing osteoclast formation. To explore the effect and mechanism of this pathway, bone marrow cells were induced to osteoclasts and treated with IL-7, a STAT5 inhibitor or supernatants from T cells. The results showed that the IL-7/IL-7R pathway played a direct inhibitory role in osteoclast differentiation via STAT5 signalling pathway in a RANKL-induced manner. We applied flow cytometry to analyse the effect of IL-7 on T-cell RANKL expression and found that IL-7/IL-7R pathway had an indirect role in the osteoclast differentiation process by enhancing the RANKL expression on T cells. In conclusion, the IL-7/IL-7R pathway exhibited a dual effect on osteoclastogenesis of CIA mice by interacting with osteoimmunology processes and could be a novel therapeutic target for autoimmune diseases such as RA.