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Expression of chemokines and chemokine receptors on peripheral blood mononuclear cells of patients with rheumatoid arthritis

Introduction. Rheumatoid arthritis (RA) is chronic joint disease marked by the persistent inflammation and osteodestruction, causing progressive disability and crippling. The mechanisms leading to joint destruction involve infiltration of inflammatory cells and T lymphocytes as well as activation of osteoclasts, multinucleated cells derived from monocyte/macrophage lineage. Human osteoclast progenitors (OCPs) are contained among peripheral blood monocytes and have been shown to be present at low frequency in healthy subjects. The accumulation of T lymphocytes and inflammatory cells at the site of inflammation involves, among others, chemokine signals. It is known that synovial tissue and synovial fluid from RA patients highly express several chemokines and, furthermore, that OCPs exhibit chemotaxis as well. The aim of our study was to define these chemotactic signals by analyzing expression of several chemokine and chemokine receptors on T lymphocytes and OCPs in the peripheral blood of RA patients. 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. The phenotype of isolated mononuclear cells was determined using flow cytometry. Expression of following chemokine receptors was analyzed on OCPs (CD3-CD19-CD56- CD11b+CD14+): C5AR1, CCR1, CCR2, CCR4, CXCR4. T lymphocytes (CD3+/CD4+ or CD3+/CD8+) were analyzed for expression of CXCR5, CCR4, CCR6 chemokine receptors. Lymphoid lineage positive (CD3+/CD19+/CD56+) population was then sorted and analyzed for the expression of the respective chemokine ligands: SDF-1/CXCL12, MIP-1α/CCL3, MIP- 1β/CCL4 and MCP-1/CCL2 by qPCR. Results. We have verified that human peripheral blood OCPs differently express chemokine receptors CCR1, CCR2, CCR4 and CXCR4. Expression of CCR4 and CXCR4 was found on approximately 10-15% of OCPs, with no difference between RA and control subjects. A small subpopulation of OCPs expressing CCR1 (under 1%) was expanded in RA patients compared to controls, whereas the proportion of CCR2+ OCPs was two-fold lower in RA patients (approximately 10%). The proportion of T lymphocytes expressing CCR4 was two-fold higher in RA patients compared to controls. T lymphocyte expression of CXCR5 and CCR6 was similar between RA and control group. Chemokine gene expression of sorted lymphoid lineage positive population from RA patients revealed two-fold higher expression of MCP-1/CCL2 compared to controls. Conclusions. Expression of several chemokine receptors is altered in RA on both OCPs and T lymphocytes, and T lymphocytes themselves exhibit altered expression of CCL2 indicating a possible specific chemotactic mechanism and environment in RA. These results may help to reveal migration mechanism of T lymphocytes and OCPs specifically associated with RA in order to develop more efficient therapeutic approaches.

chemokines; chemokine receptors; lymphocytes; osteoclast progenitors; rheumatoid arthritis

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