Background Involvement of the complement system in the pathogenesis of rheumatoid arthritis (RA) has been proposed, as complement activation correlate with disease activity1. More specifically, C5a levels were elevated in synovial fluid (SF) from RA patients2, and blockade of C5a receptor (C5aR)-signaling was efficacious in animal models of arthritis3.
Objectives To confirm C5a elevation in SF from RA patients and investigate the C5a levels in SF from psoriatic arthritis (PsA) patients. Moreover, to investigate the expression of (C5aR) on leukocytes in inflamed joints. Finally, to demonstrate ex vivo effects of C5aR-blockade both on leukocyte migration and cytokine release.
Methods C5a levels were determined by ELISA. Immunohistochemistry was performed on synovial biopsies from patients and controls without arthritis. The effect of a blocking anti-human C5aR mAb on leukocyte migration was determined using a Boyden chamber system. The effect on cytokine release from co-cultures of cytokine-stimulated T cells (Tcks) and monocyte-derived macrophages was determined by multiplex cytokine assay.
Results C5a levels were increased in both RA and PsA SF relative to SF from osteoarthritis (OA) patients. Infiltrating C5aR-positive (C5aR+) cells were detected in 7 out of 8 patients with RA, and in 10 out of 10 patients with PsA, but not in control synovium (n=5). C5aR+ cells were primarily polymorphonuclear leukocytes (PMNs) and macrophages. C5aR+ macrophages were mainly found in lymphoid aggregates in close contact to T cells. In the Tck:macrophage co-cultures, anti-C5aR inhibited spontaneous TNFα release in 5 out of 6 patients. Ex vivo PMN migration to SFs from RA patients was attenuated by anti-C5aR mAb for 5 out of 7 SF donors resulting in 25%–100% reduction in migration. Monocyte migration to SFs from RA patients was attenuated by anti-C5aR mAb in 3 out of 6 SFs resulting in 47%–100% reduction in migration. For 3 out of 5 PsA patient SFs PMN migration to SFs was completely inhibited by anti-C5aR mAb.
Conclusions Elevated levels of C5a in RA patient SF was confirmed. We demonstrated C5aR expression on PMNs and macrophages in synovial tissue, and that only macrophages in contact with T cells express C5aR. We also showed for the first time elevation of SF C5a and infiltration of C5aR+ cells in patients with PsA. These descriptive data were supplemented with functional data demonstrating that PMN and monocyte migration towards SF from both patient groups is inhibited by a blocking anti-C5aR mAb, and that this mAb also inhibits spontaneous cytokine release from co-cultures of Tcks and macrophages. Thus, blocking C5aR might be a beneficial treatment for patients with RA and PsA.
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Song, JJ et al. (2011) J Clin Invest, 121, 3517-3527
Lee, H et al. (2006) Nat Biotech, 24, 1279-1284
Disclosure of Interest L. Hornum Shareholder of: Novo Nordisk A/S, Employee of: Novo Nordisk A/S, A. Hansen Shareholder of: Novo Nordisk A/S, Employee of: Novo Nordisk A/S, D. Tornehave Shareholder of: Novo Nordisk A/S, Employee of: Novo Nordisk A/S, K. Håkansson Shareholder of: Novo Nordisk A/S, Employee of: Novo Nordisk A/S, M. Fjording Shareholder of: Novo Nordisk A/S, Employee of: Novo Nordisk A/S, E. Bartels: None Declared, N. Søe: None Declared, H. Bliddal: None Declared