Abstract
1073
Objectives It is difficult to find a reliable biomarker to monitor tolerance graft accurately. Toll-like receptor 5 (TLR5), the only protein recognition receptor of TLRs, is an immune regulation target potentially related with immunosuppressant rapamycin. This study was designed to determine whether TLR5 could be a biomarker for in vivo allograft visualization after rapamycin treatment, using radiolabeled sodium iodide (131I)-anti-TLR5 monoclonal antibody (mAb).
Methods BALB/c mice were transplanted with C57BL/6 skin were divided into the rapamycin-treated group and the phosphate buffered saline [PBS]-rejection group, respectively. In vivo dynamic whole-body phosphor-autoradiography and ex vivo biodistribution studies were conducted after 131I-anti-TLR5 mAb injection.
Results Dynamic phosphor-autoradiography imaging showed clear graft localization from 12 h onward. At 72 h after injection, graft uptake quantified from images was higher for the rapamycin-treated group (26,448 ± 904 digital light units [DLU]/mm2), compared with the PBS-treated allo-rejection group (9176 ± 576 DLU/mm2). Pre-treatment with anti-TLR5 mAb blocked graft uptake. In addition to the non-specific control, 131I labeled mouse IgG provides evidence that 131I-anti TLR5 mAb binds primarily to TLR5 present in the graft area.Organ biodistribution study reflected the same tendency, and 131I-anti-TLR5 mAb uptake reached a maximum of 12.05 ± 1.86 %ID/g (percent injected dose per gram) at 1 h, and graft-to-native skin ratio reached 8.10 ± 0.10 %ID/g at 72 h after injection in rapamycin-treated grafts. Immunohistochemistry results supported the dynamic phosphor-autoradiographagy and ex vivo biodistrbution studies.
Conclusions Radiolabeled anti-TLR5 mAb is a new tracer for non-invasive in vivo imaging of TLR5 in rapamycin-treated allograft.