Laboratory of Immunobiology, Rega Institute, Katholieke Universiteit Leuven, Leuven, Belgium.
J Nucl Med. 2013 May;54(5):807-14. doi: 10.2967/jnumed.112.111781. Epub 2013 Feb 27.
Rheumatoid arthritis (RA) is a chronic autoimmune disease occurring in approximately 1% of the worldwide population. The disease primarily affects the joints, where inflammatory cells, such as macrophages, invade the synovium and cause cartilage and bone destruction. Currently, it is difficult to efficiently diagnose and monitor early-stage RA. In this study, we investigated whether SPECT/micro-CT imaging with (99m)Tc-labeled Nanobodies directed against the macrophage mannose receptor (MMR) is a useful tool for monitoring and quantifying joint inflammation in collagen-induced arthritis (CIA), a mouse model for RA. The expression of MMR was analyzed on macrophages and osteoclasts generated in vitro and in cells obtained from various organs from mice with CIA.
CIA was induced in DBA/1 mice by injection of collagen type II in complete Freund adjuvant, and cell suspensions from the inflamed joints and other organs were obtained. Macrophages and osteoclasts were generated in vitro from bone marrow cells. Expression of MMR was quantified by quantitative polymerase chain reaction and flow cytometry with specific Nanobodies and conventional antibodies. SPECT/micro-CT imaging was performed with (99m)Tc-labeled MMR and control Nanobodies.
MMR was highly expressed on macrophages and to a lesser extent on osteoclasts generated in vitro. In mice with CIA, MMR expression was detected on cells from the bone marrow, lymph nodes, and spleen. In synovial fluid of arthritic joints, MMR was expressed on CD11b(+)F4/80(+) macrophages. On in vivo SPECT/micro-CT imaging with consecutive injections of MMR and control Nanobodies, a strong MMR signal was seen in the knees, ankles, and toes of arthritic mice. Quantification of the SPECT imaging confirmed the specificity of the MMR signal in inflamed joints as compared with the control Nanobody. Dissection of the paws revealed an additional significant MMR signal in nonarthritic paws of affected mice (i.e., mice displaying symptoms of arthritis in other paws).
Our data show that MMR is expressed on macrophages in vitro and in vivo in synovial fluid of inflamed paws, whereas expression is relatively low in other tissues. The use of Nanobodies against MMR in SPECT/micro-CT imaging generates the possibility to track inflammatory cells in vivo in arthritic joints.
类风湿关节炎（RA）是一种慢性自身免疫性疾病，约占全球人口的 1%。该疾病主要影响关节，炎症细胞如巨噬细胞浸润滑膜，导致软骨和骨破坏。目前，RA 的早期诊断和监测较为困难。在这项研究中，我们研究了针对巨噬细胞甘露糖受体（MMR）的（99m）Tc 标记纳米抗体 SPECT/微 CT 成像是否可用于监测和定量胶原诱导关节炎（CIA）模型鼠关节炎症，CIA 是一种 RA 小鼠模型。我们分析了体外生成的巨噬细胞和破骨细胞以及 CIA 小鼠各器官来源细胞中 MMR 的表达。
通过在完全弗氏佐剂中注射 II 型胶原诱导 DBA/1 小鼠 CIA，获得炎性关节和其他器官的细胞悬液。从骨髓细胞体外生成巨噬细胞和破骨细胞。通过定量聚合酶链反应和流式细胞术，用特异性纳米抗体和常规抗体检测 MMR 的表达。用（99m）Tc 标记的 MMR 和对照纳米抗体进行 SPECT/微 CT 成像。
MMR 在体外生成的巨噬细胞上高度表达，在破骨细胞上表达程度较低。在 CIA 小鼠中，MMR 在骨髓、淋巴结和脾脏的细胞上表达。在关节炎关节的滑液中，MMR 在 CD11b（+）F4/80（+）巨噬细胞上表达。在关节炎小鼠连续注射 MMR 和对照纳米抗体的 SPECT/微 CT 成像中，膝关节、踝关节和脚趾有强烈的 MMR 信号。SPECT 成像定量分析证实了与对照纳米抗体相比，在炎性关节中 MMR 信号的特异性。对爪子的解剖显示，受影响小鼠的非关节炎爪子（即其他爪子出现关节炎症状的小鼠）也存在明显的 MMR 信号。
我们的数据表明，MMR 在体外和体内关节炎性爪子的滑膜液中表达于巨噬细胞，而在其他组织中的表达水平较低。用针对 MMR 的纳米抗体进行 SPECT/微 CT 成像，可在体内活体追踪关节炎关节中的炎症细胞。
