Cy3-tilmanocept labeling of macrophages in joints of mice with antibody-induced arthritis and synovium of human patients with rheumatoid arthritis.

γ-Tilmanocept (99m Tc-tilmanocept) is a receptor-directed, radiolabeled tracer that is FDA-approved for guiding sentinel lymph node biopsy. Tilmanocept binds the C-type lectin mannose receptor (MR, CD206) on macrophages. In this work, non-radioactive, fluorescently-labeled Cy3-tilmanocept was used to detect CD206+ mononuclear cells in cartilage of mice with antibody-induced arthritis and in synovial fluid and tissue of human subjects with rheumatoid arthritis (RA) for comparison to osteoarthritis (OA), and healthy volunteer (HV) controls. Murine arthritis was induced by injection of monoclonal anti-cartilage antibody followed by injection of E. coli lipopolysaccharide. Post-arthritis development (7-11 days), mice were injected intravenously with Cy3-tilmanocept followed by in vivo and ex vivo epifluorescence imaging. Two-photon imaging, immunofluorescence, and immunohistochemistry were used to identify articular and synovial macrophages (CD206, F4/80, and Cy3-tilmanocept binding) in murine tissues. Cy3-tilmanocept epifluorescence was present in arthritic knees and elbows of murine tissues; no radiographic changes were noted in the skeletons. However, inflammatory arthritic changes were apparent by histopathology and immunohistochemistry (F4/80), immunofluorescence (CD206) and Cy3-tilmanocept binding. In human RA synovial fluid, Cy3-tilmanocept staining correlated with CD206+/CD16+ cells; negligible labeling was observed in OA samples. Cy3-tilmanocept co-localized with CD206 and staining was significantly higher in RA synovial tissue compared to OA or HV. Our results demonstrate that imaging with Cy3-tilmanocept can detect in vivo inflammatory, CD206+ macrophages in an early arthritis animal model and in human RA patients. These data establish a novel tool for pre-clinical research of early arthritis and have implications for early RA detection and monitoring of therapeutic efficacy in humans. This article is protected by copyright. All rights reserved.