gms | German Medical Science

Background: Rheumatoid Arthritis (RA) is an autoimmune inflammatory disease characterized by inflammatory destruction of articular cartilage and juxtaarticular bone, which is mediated on the cellular level by RA synovial fibroblasts and osteoclasts. Natural killer (NK) cells have been proposed recently to be involved in the process of joint destruction in RA.

Methods: Synovial fluid and blood samples were obtained from patients with RA and blood samples from healthy individuals. Informed consent was obtained from all donors. Mononuclear cells were isolated by Ficoll density gradient centrifugation and consecutive MACS separation of CD14+ monocytes and CD56+CD3– NK cells. Monocytes were cultured in 24-well plates in the presence of sRANKL and M-CSF as positive control, in medium as negative control, and co-cultured with NK cells for analysis of their influence on osteoclastogenesis and of potential modulation of this effect by different soluble factors. Osteoclats were identified by TRAP staining (Sigma- Aldrich) and calcified matrix resorption using osteoassays (Corning) according to the manufacturers’ instructions.

Results: Co-culture of monocytes with NK cells resulted in a significant induction of osteoclastogenesis as compared to the negative control. The efficacy of induction of osteoclastogenesis by co-culture with NK cells reached up to 50% of the effect of monocyte culture in the presence sRANKL and M-CSF (positive control). This effect was only observed with cells from RA patients but not from healthy controls. The effect of NK cells on osteoclastogenesis was enhanced by addition of TNF, IL-1ß and, remarkably, adiponectin.

Conclusion: NK-cells from RA patients exert a significant effect on osteoclastogenesis from monocyte precursors in vitro which is amplified by different soluble factors that are found in the inflammatory milieu of arthritic joints. Thus, NK cells could play an important role in the osteodestructive process of RA.