The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, 1550 Orleans St. CRB2 493, Baltimore, MD, 21228, USA.
Center for Infection and Inflammation Imaging Research, Department of Pediatrics, Johns Hopkins University, Baltimore, MD, 21228, USA.
Mol Imaging Biol. 2019 Jun;21(3):473-481. doi: 10.1007/s11307-018-1228-5.
Diagnosis and therapeutic monitoring of chronic bacterial infection requires methods to detect and localize sites of infection accurately. Complement C3 activation fragments are generated and covalently bound to selective bacterial pathogens during the immune response and can serve as biomarkers of ongoing bacterial infection. We have developed several probes for detecting tissue-bound C3 deposits, including a monoclonal antibody (mAb 3d29) that recognizes the tissue-bound terminal processing fragments iC3b and C3d but does not recognize native circulating C3 or tissue-bound C3b.
To determine whether mAb 3d29 could be used to detect chronic Mycobacterium tuberculosis infection non-invasively, aerosol-infected female C3HeB/FeJ mice were injected with [I]3d29 mAb and either imaged using single-photon emission computed tomography (SPECT)/X-ray computed tomography (CT) imaging at 24 and 48 h after radiotracer injection or being subjected to biodistribution analysis.
Discrete lesions were detected by SPECT/CT imaging in the lungs and spleens of infected mice, consistent with the location of granulomas in the infected animals as detected by CT. Low-level signal was seen in the spleens of uninfected mice and no signal was seen in the lungs of healthy mice. Immunofluorescence microscopy revealed that 3d29 in the lungs of infected mice co-localized with aggregates of macrophages (detected with anti-CD68 antibodies). 3d29 was detected in the cytoplasm of macrophages, consistent with the location of internalized M. tuberculosis. 3d29 was also present within alveolar epithelial cells, indicating that it detected M. tuberculosis phagocytosed by other CD68-positive cells. Healthy controls showed very little retention of fluorescent or radiolabeled antibody across tissues. Radiolabeled 3d29 compared with radiolabeled isotype control showed a 3.5:1 ratio of increased uptake in infected lungs, indicating specific uptake by 3d29.
3d29 can be used to detect and localize areas of infection with M. tuberculosis non-invasively by 24 h after radiotracer injection and with high contrast.
慢性细菌感染的诊断和治疗监测需要能够准确检测和定位感染部位的方法。补体 C3 激活片段在免疫反应过程中产生并与选择性细菌病原体共价结合，可作为持续细菌感染的生物标志物。我们已经开发了几种用于检测组织结合 C3 沉积物的探针，包括一种单克隆抗体 (mAb 3d29)，它识别组织结合的末端加工片段 iC3b 和 C3d，但不识别天然循环 C3 或组织结合的 C3b。
为了确定 mAb 3d29 是否可用于非侵入性检测慢性结核分枝杆菌感染，将气溶胶感染的雌性 C3HeB/FeJ 小鼠注射 [I]3d29 mAb，并在放射性示踪剂注射后 24 和 48 小时使用单光子发射计算机断层扫描 (SPECT)/X 射线计算机断层扫描 (CT) 成像进行成像，或进行生物分布分析。
SPECT/CT 成像在感染小鼠的肺部和脾脏中检测到离散病变，与感染动物 CT 检测到的肉芽肿位置一致。未感染小鼠的脾脏中出现低水平信号，健康小鼠的肺部未见信号。免疫荧光显微镜显示，感染小鼠肺部的 3d29 与巨噬细胞聚集物（用抗 CD68 抗体检测到）共定位。3d29 在巨噬细胞质中被检测到，与内化的结核分枝杆菌的位置一致。3d29 也存在于肺泡上皮细胞中，表明它检测到被其他 CD68 阳性细胞吞噬的结核分枝杆菌。健康对照者在整个组织中保留的荧光或放射性标记抗体很少。与放射性标记的同种型对照相比，放射性标记的 3d29 在感染的肺部显示出 3.5:1 的摄取增加比值，表明 3d29 的特异性摄取。
在放射性示踪剂注射后 24 小时内，3d29 可用于非侵入性检测和定位结核分枝杆菌感染部位，并具有高对比度。
