Background Disease activity and response to therapy in RA correlates with changes in synovial macrophage numbers and their products. M-CSF or interleukin (IL)-34 stimulation of their common receptor CSFR1 promotes macrophage differentiation, activation and osteoclastogenesis, but M-CSF and IL-34 play distinct roles in murine development. Pharmacological inhibition of CSFR1 is beneficial in animal models of arthritis but the relative contributions of M-CSF, IL-34 and their receptor to inflammation in rheumatoid arthritis (RA) are unknown.
Objectives To determine the roles of M-CSF and IL-34 in huma macrophage activation, and human and murine models of RA.
Methods M-CSF, IL-34, and cellular markers were detected by immunohistochemistry and digital image analysis in synovial tissue from 18 biological-naïve RA patients, 14 PsA patients, and 4 controls without inflammatory disease (2 healthy donors and 2 OA patients). Gene expression in M-CSF and IL-34 –differentiated human macrophages was assessed by FACS analysis and q-PCR arrays. RA synovial explants were incubated with M-CSF, IL-34, control antibody (Ab), or a humanized CSFR1-blocking Ab. Prophylactic effects of control and CSFR1-blocking Ab were examined in murine collagen-induced arthritis (CIA).
Results Expression of M-CSF and IL-34 was similar in RA and PsA synovial tissue, but lower in controls (p< 0.05). M-CSF expression was restricted to ECs and IL-34 was observed in sublining mononuclear cells and intimal lining layer cells. CXCL5, CXCL6, FN1, COL1A1, COL6A1-2, COL14A1, COL15A1, MMP7, MMP8 and MMP9 mRNA expression was significantly upregulated in macrophages differentiated in M-CSF compared to IL-34, while CXCL7, CXCL9, CXCL10, CXCL11, CXCL12, LAMA1, and MMP2 were downregulated. M-CSF or IL-34 had no effect on RA synovial explant IL-6 production, but anti-CSFR1 Ab dose-dependently reduced IL-6 production. Treatment with anti-CSFR1 Ab in CIA significantly reduced paw swelling and joint destruction.
Conclusions M-CSF and IL-34 are expressed in topographically distinct regions of inflamed synovial tissue and differentially effect macrophage capacity to attract inflammatory cells and remodel tissue. Simultaneous inhibition of CSFR1 interactions with both M-CSF and IL-34 suppresses inflammatory activation of RA synovial tissue and pathology in CIA, suggesting a novel therapeutic strategy for RA.
Disclosure of Interest S. Garcia: None Declared, L. Hartkamp: None Declared, M. W. Tang: None Declared, I. van Es: None Declared, H. Lin Shareholder of: stock options in Five Prime Therapeutics, Inc., Employee of: Five Prime Therapeutics, Inc., L. Long Shareholder of: stock options in Five Prime Therapeutics, Inc., Employee of: Five Prime Therapeutics, Inc., E. Masteller Shareholder of: stock options in Five Prime Therapeutics, Inc., Employee of: Five Prime Therapeutics, Inc., B. Wong Shareholder of: stock options in Five Prime Therapeutics, Inc., Employee of: Five Prime Therapeutics, Inc., P. Tak Employee of: GlaxoSmithKline, K. Reedquist Grant/research support from: Five Prime Therapeutics, Inc.