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Inflammatory cell infiltration and synovial activation are important processes in rheumatoid arthritis. Chemotactic gradients of various chemokines are responsible for cell attraction and possibly for their activation. We have previously detected strong expression of chemokine receptor CXCR3 in the rheumatoid joint by immunostaining.
Characterization of the cells expressing CXCR3 in RA synovial membrane.
Synovial tissue samples were obtained from RA patients undergoing synovectomy or a total joint replacement. Cells were released by digestion with collagenase, DNAse and briefly with hyaluronidase. A three colour fluorescence analysis was performed with FITC conjugated anti-CXCR3 mouse MAb (R&D) and with a panel of phycoerythrin (PE) conjugated MAb (anti-CD3, CD4, CD8, CD19, CD55, CD31, CD68, CD14 and CD45). Live cells were identified by propidium iodide. PBCs were stained using the same protocol.
As expected, a proportion of CD3+ and CD4+ blood and synovial cells were CXCR3 positive. In addition, CXCR3 was also seen in synovial cells positive for CD55, CD14, CD8 and to a lesser extent CD31. However, in contrast to the surface staining of cells from peripheral blood, synovial cells displayed only intracellular staining for CXCR3. No CXCR3 staining could be detected on the surface of any type of viable synovial cell, including CD3 positive lymphocytes.
Flow cytometry identifies synovial cells that display intracellular CXCR3 staining. These cells are comprised of T lymphocytes, macrophages, possibly synovial fibroblasts and endothelial cell populations. The intracellular presence of CXCR3 suggests a possible internalization of this molecule, which may be a consequence of ligand binding. The significance of this phenomenon and of CXCR3 expression in cell types other than leukocytes remains to be determined.
This work is supported by a grant NI/6459 from IGA MZ CR.