SAT0553 Correlation of the Frequency and Differentiation Potential of Osteoclast Progenitor Cells with Disease Activity and Response to Therapy in Patients with Rheumatoid Arthritis

Background Rheumatoid arthritis (RA) is marked by the persistent inflammation and osteodestruction, causing progressive disability. The mechanisms leading to joint destruction involve differentiation and activation of osteoclasts, multinucleated cells derived from monocyte/macrophage lineage. Human osteoclast progenitors (OCPs) represent a subpopulation of peripheral blood monocytes and have been shown to be present at low frequency in the peripheral blood of healthy subjects and arthritic patients. Objectives The aim of our study was to analyze the phenotype, frequency and osteoclastogenic potential of OCPs in the peripheral blood and synovial fluid of RA patients compared with peripheral blood OCPs of healthy controls. In addition, results were correlated with clinical data, including inflammatory indicators and variables describing disease activity and severity. Methods Mononuclear cells were isolated from peripheral blood of healthy controls and RA patients, after obtaining approval from the Ethical Committee and informed consent from patients. A subset of peripheral blood and synovial fluid samples were collected from RA patients prior and in the follow-up of TNF-blockage treatment. The phenotype of isolated mononuclear cells was determined within peripheral blood and synovial fluid mononuclear cells using flow cytometry for the following surface markers: CD3, CD11b, CD14, CD16, CD19, CD56, CD115, CCR1, CCR2, CCR4. Lymphoid lineage negative (CD3-CD19-CD56-) population expressing myeloid markers (CD11b/CD14) was then sorted and cultured with the addition of macrophage colony-stimulating factor (M-CSF; 30 ng/mL) and receptor activator of nuclear factor-kappa-B ligand (RANKL; 60 ng/mL) for two weeks to stimulate osteoclast differentiation. Osteoclasts were detected by cytochemical staining for tartrate-resistant acid phosphatase. In addition, expression of chemokine receptors was profiled in order to determine the migratory properties of putative osteoclast progenitor subpopulations. Results We have verified that peripheral blood and synovial fluid samples of RA patients contain an osteoclastogenic population bearing the phenotype CD3-CD19-CD56-CD11b+CD14+. A proportion of cells within this population also express myeloid markers (CD115 and CD16) and different chemokine receptors. This osteoclastogenic population is significantly increased in RA patients, comprising 2.5-5.5% of circulating mononuclear cells compared to approximately 1.5% in healthy contr