Ultrasound molecular imaging of M2 macrophages for early detection of chronic rejection in heart transplantation

Chronic rejection (CR) remains the leading cause of morbidity and mortality in heart transplantation survivors. The primary pathological features of CR encompass cardiac allograft vasculopathy and myocardial fibrosis. Currently, its diagnosis heavily relies on invasive procedures, underscoring the pressing need for non-invasive evaluation methods. This study introduces a novel approach utilizing mannose-modified microbubbles (MB_man) targeting CD206 (mannose receptor) positive M2 macrophages for early CR detection. In vitro experiments demonstrate substantial adhesion of MB_man to M2 macrophages compared to common microbubbles (MB_con). In a CR rat model, MB_man and MB_con are administered at three distinct time points (2 weeks, 4 weeks, and 6 weeks), followed by contrast-enhanced ultrasound images and quantitative analysis using the ultrasound destruction-supplementation method. Starting at 2 weeks and continuing through 6 weeks, MB_man demonstrates significantly higher signal intensity than MB_con in allograft rats. However, this difference is not observed in isograft rats at any of the indicated time points. These findings suggest an increase in M2 macrophage infiltration in allografts compared to isografts. Furthermore, the signal intensity of MB_man positively correlates with the percentage of CD206 in allograft rats. This study proposes a promising approach, simultaneous noninvasive ultrasound molecular imaging, for the early-stage evaluation of CR.