Diagnosis of arthritis using near-infrared fluorochrome Cy5.5

Purpose: Near-infrared range fluorescence (NIRF) imaging is a potential tool to diagnose biologic processes in vivo. This applicability study sought to define whether imaging with fluorochrome Cy5.5 can identify arthritis in murine antigen-induced arthritis (AIA). Materials and Methods: On day 7 of AIA (n = 9 mice), fluorescence intensities in inflamed and contralateral knee joints (the latter as internal control) were measured before and after intravenous injection of Cy5.5 (until 72 hours). Cy5.5 joint deposition was verified by confocal laser-scanning microscopy. Dye phagocytosis was evaluated in cultured macrophages (cell line PMJ2-R) by FACS analysis. Cy5.5 binding to serum protein was tested by NIRF scanning and gel electrophoresis. Results: Between 2 and 72 hours, the arthritic knee joints showed significantly higher fluorescence intensities compared with contralateral joints. Microscopy confirmed Cy5.5 deposition in the synovial membrane. Cultured macrophages actively phagocytosed Cy5.5. Cy5.5 bound mainly to albumin as the main serum protein. Conclusion: NIRF imaging with Cy5.5 can identify arthritic joints in vivo, likely due to nonspecific deposition.