SPECT/CT Imaging of Mycobacterium tuberculosis Infection with [125I]anti-C3d mAb

• Published in: Molecular imaging and biology 2019-06, Vol.21 (3), p.473-481
• Main Authors: Foss, Catherine A., Kulik, Liudmila, Ordonez, Alvaro A., Jain, Sanjay K., Michael Holers, V., Thurman, Joshua M., Pomper, Martin G.
• Format: Article
• Language: English
• Subjects: Aerosols; Alveoli; Animals; Antibodies, Monoclonal - metabolism; Bacteria; Bacterial infections; Biomarkers; Chronic infection; Complement activation; Complement C3 - immunology; Complement component C3; Complement component C3b; Computation; Computed tomography; Cytoplasm; Epithelial cells; Female; Fluorescence; Fragments; Imaging; Immune response; Immune system; Immunofluorescence; Immunoglobulin G - metabolism; Infections; Injection; Iodine Radioisotopes - chemistry; Lesions; Lung - diagnostic imaging; Lung - microbiology; Lung - pathology; Lungs; Macrophages; Medical imaging; Medicine; Medicine & Public Health; Mice; Microscopy; Monoclonal antibodies; Mycobacterium tuberculosis; Mycobacterium tuberculosis - physiology; Photon emission; Radioactive tracers; Radiology; Research Article; Single photon emission computed tomography; Single Photon Emission Computed Tomography Computed Tomography; Tissue Distribution; Tissues; Tuberculosis; Tuberculosis - diagnostic imaging; Tuberculosis - microbiology; Tuberculosis - pathology
• ISSN: 1536-1632; 1860-2002
• DOI: 10.1007/s11307-018-1228-5

Purpose 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. Procedures 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 [ 125 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. Results 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. Conclusion 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.