Background/Purpose:

The synovial tissue of rheumatoid arthritis (RA) patients exhibits abundant expression of CCL21, produced excessively by RA fibroblasts and macrophages. While CCR7 mediates CCL21-driven T cell migration, we previously identified a novel angiogenic function of CCL21 in RA as well. We now reveal that in RA, macrophage expression of CCR7 is significantly increased, which further supports the importance of the CCL21/CCR7 pathway. In this study, we aim to determine the range of CCL21/CCR7 function and explore its activity on CCR7+ macrophages, contributing to the progression of inflammatory and destructive RA.

Methods:

Expression of CCR7 on healthy (NL) versus RA immune cells was examined by flow cytometry and quantitative PCR. To evaluate CCL21-stimulated myeloid cell behavior, we performed monocyte chemotaxis, osteoclastogenesis assays and Western blot analysis for signaling. We also defined macrophage polarization through flow cytometry and ELISA. Intra-articular adenoviral delivery of CCL21 in mice was used to evaluate and confirm the arthritic effects of CCL21 in vivo.

Results:

The percentage of double-positive CD14+CCR7+ is 2-fold higher in macrophages derived from RA compared to NL peripheral blood (NL: 19.38 ± 2.7 %; RA: 43.14 ± 2.2 %). We find that in vitro M1 polarized cells express higher levels of CCR7, which corroborates the high expression of CCR7 on macrophages isolated from RA synovial fluid. Confirming the clinical significance of CCL21/CCR7, monocyte chemotaxis induced by RA synovial fluid is considerably reduced in the presence of either anti-CCR7 or anti-CCL21 neutralizing antibody. Recombinant CCL21 stimulates RA monocyte chemotaxis dose-dependently, through CCR7 and activation of NFκB, ERK and MAPK p38 signaling. CCL21 also affects myeloid cell differentiation and polarization. We observed an increase of M1 polarized macrophages upon CCL21 stimulation. Additionally, CCL21 ligation to CCR7 promotes osteoclast formation. Accordingly, local expression of CCL21 induces joint swelling and osteoclastic bone erosion in wild type mice, but not in CCR7-deficient mice. Histological analysis demonstrates that F4/80+ cell numbers are elevated in CCL21-treated arthritic joints. iNOS expression in the joint is increased 36-fold by CCL21. Elevated intra-articular production of M1-associated inflammatory factors confirms that local CCL21 expression promotes macrophage polarization to an M1 phenotype. We also noted that TRAP+ osteoclast numbers are 10-fold higher in CCL21 arthritic mice compared to the placebo non-arthritic group.

Conclusion:

Our findings emphasize the diverse function of CCL21 and CCR7, increased even more by the pathogenic upregulation of CCR7 expression on RA macrophages. Given that CCL21/CCR7 activation potentiates RA joint inflammation, destruction and neovascularization, this pathway may be an attractive target for therapy.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-ccl21-ccr7-axis-drives-vascular-inflammatory-and-destructive-remodeling-in-rheumatoid-arthritis/