RA synovial macrophages also expressed the type I transmembrane protein V-set and Ig domain-containing 4 (Vsig4): near-infrared fluorescence (NIRF) imaging of Cy7-labeled anti-Vsig4 Nbs showed the accumulation of Vsig4+ macrophages in the joint of CIA mice. Here, VSIG4 is linked to rheumatoid arthritis.