μPET/CT imaging of experimental autoimmune nephritis using 64Cu-αCD11b

Objectives: The purpose of this study was to develop PET tracer targeting myeloid cells and to noninvasively assess experimental autoimmune nephritis by tracking infiltration of CD11b+ inflammatory cells. Methods: Mice (129x1/svJ, female) were challenged with rabbit IgG and complete Freund's adjuvant (250 µL) through i.p. injection at day 0, followed by i.v. injection of anti-glomerular basement membrane (GBM) serum (160 µL/20 g) at day 5. Anti-mouse CD11b antibody (αCD11b) was conjugated with DOTA and then labeled with 64Cu. μPET/CT images with 64Cu-DOTA-αCD11b (64Cu-αCD11b) were acquired at day 14. Normal mice were used as a control. Urine and blood samples were collected for biochemical test. Major organs were collected, weighted, and counted for radioactivity. Kidneys were also collected for autoradiography and immunohistochemical (IHC) examinations. Results: 64Cu-αCD11b bound specifically to CD11b+ myeloid cells, which had been confirmed by bone marrow cell binding assay in vitro and μPET imaging of CD11b-knockout mice in vivo. μPET-CT images showed that in normal mice, high 64Cu-αCD11b uptake was seen in bone marrow in the spinal cord, femur, tibia, scapula and humerus. Significant activity was also found in the spleen. 64Cu-αCD11b showed significantly higher uptake in the kidney of mice with autoimmune nephritis (19.5 ± 2.9 %ID/g) than the kidneys of normal mice (5.9 ± 0.5 %ID/g) (p < 0.001). In addition, autoradiography showed that 64Cu-αCD11b was primarily retained in the renal cortex in the mice with nephritis. Moreover, IHC staining confirmed that the kidney of mice with nephritis had greater numbers of infiltrating CD11b+F4/80+ macrophages in the glomerular regions of renal cortex than the normal mice did. Whole body μPET-CT imaging of mice with 64Cu-αCD11b showed that the uptake of 64Cu-αCD11b in the bone marrow significantly increased in nephritic mice (21.5 ± 7.88 %ID/g) compared to normal mice (9.3 ± 1.84 %ID/g) (p