Near-infrared lymphography as a minimally invasive modality for imaging lymphatic reconstitution in a rat orthotopic hind limb transplantation model

Wider application of vascularized composite allotransplantation (VCA) is limited by the need for chronic immunosuppression. Recent data suggest that the lymphatic system plays an important role in mediating rejection. This study used near-infrared (NIR) lymphography to describe lymphatic reconstitution in a rat VCA model. Syngeneic (Lewis-Lewis) and allogeneic (Brown Norway-Lewis) rat orthotopic hind limb transplants were performed without immunosuppression. Animals were imaged pre- and postoperatively using indocyanine green (ICG) lymphography. Images were collected using an NIR imaging system. Co-localization was achieved through use of an acrylic paint/hydrogen peroxide mixture. In all transplants, ICG first crossed graft suture lines on postoperative day (POD) 5. Clinical signs of rejection also appeared on POD 5 in allogeneic transplants, with most exhibiting Grade 3 rejection by POD 6. Injection of an acrylic paint/hydrogen peroxide mixture on POD 5 confirmed the existence of continuous lymphatic vessels crossing the suture line and draining into the inguinal lymph node. NIR lymphography is a minimally invasive imaging modality that can be used to study lymphatic vessels in a rat VCA model. In allogeneic transplants, lymphatic reconstitution correlated with clinical rejection. Lymphatic reconstitution may represent an early target for immunomodulation.