Loss of surface CXCR3 expression in the RA synovial CD3 cells as a result of ligand binding suggests the mechanism for increased Th1 cell infiltration

Introduction

Inflammatory cell infiltration in synovium is a characteristic feature of rheumatoid arthritis (RA). Chemotactic gradients of various chemokines are responsible for cell attraction and possibly for their activation. Th1 cells are the predominant T cells in the synovium and have been shown to express high levels of chemokine receptors CXCR3 and CCR5.

Aim

To examine a role of CXCR3 and its respective ligands (IP-10 and MIG) in the migration of Th1 cells into the synovial tissue.

Methods

Synovial tissue samples were obtained from 12 RA patients undergoing either 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 MAb (R&D) and with PE conjugated anti-CD3. Live cells were identified by propidium iodide. PBCs were stained using the same protocol. Cells were permeabilized with IntraPrep for intracellular staining. Cryostat tissue sections were stained for CXCR3 ligands IP-10 and MIG.

Results

In the investigated RA patients 18–70% of PB CD3⁺ cells expressed surface CXCR3. CD3⁺ population of cells in the synovium expressed 0–5% of surface CXCR3. The intracellular CXCR3 was found in 97–100% of synovial CD3⁺ cells. IP-10 and MIG were expressed in all tissue samples. This staining was particularly enhanced in tissues with strong vascularity. Endothelial cells were strongly positive for IP-10 and weakly positive for MIG.

Conclusions

The intracellular presence of CXCR3 and simultaneous loss of surface expression in the synovial CD3⁺ cells is the result of internalization of this molecule upon ligand binding. The presence of IP-10 and MIG in the synovium suggests the possible method of Th1 cell migration and their further activation.