Up-regulation of XCR1 expression in rheumatoid joints

Chemokine receptor-positive cells play a crucial role in controlling synovitis in rheumatoid arthritis (RA). We studied 16 chemokine receptors of the CC, CXC, CX3C and C families by analysing venous blood and synovial fluid samples and synovial tissues from RA patients.

Mononuclear cells (MNCs) in paired synovial fluid and venous blood samples from 7 RA patients were studied for the expression of CCR1 to 9, CXCR1 to 5, CX3CR1 and XCR1 by quantitative reverse transcription polymerase chain reaction (RT-PCR). Expression of chemokine receptors on synovial tissues from 9 RA patients were examined by in situ hybridization. Levels of chemokines were measured by enzyme-linked immunosorbant assay.

Higher expression levels of XCR1 and CCR5 in MNCs from synovial fluid, as compared with those from venous blood, were consistently demonstrated in all RA patients (P<0.01). Through in situ hybridization, XCR1 expression was detected in infiltrating MNCs and synoviocytes in synovial tissues. Levels of lymphotactin, the ligand of XCR1, were significantly higher in the joint fluid than those in the paired serum samples (P<0.01).

We found an up-regulation of XCR1 expression in MNCs from the rheumatoid joint, and detected XCR1 expression in infiltrating MNCs in synovial tissues, as well as increased lymphotactin levels in synovial fluid. XCR1-positive cells may play a role in rheumatoid joints.