Leukocyte-Targeted Myocardial Contrast Echocardiography Can Assess the Degree of Acute Allograft Rejection in a Rat Cardiac Transplantation Model

Abstract

Background-Repetitive endomyocardial biopsies are necessary to monitor the effects of immunosuppressants after cardiac transplantation. Contrast ultrasound with microbubble targeting of leukocytes detects acute leukocyte infiltration. We examined whether leukocyte-targeted myocardial contrast echocardiography (MCE) could provide for the quantitative assessment of acute cardiac rejection. Methods and Results-Hearts from Brown Norway rats or Lewis rats were transplanted into other Brown Norway rats. Isografts and groups of allografts either untreated or treated with cyclosporin A (CsA) at a low dose (3 mg · kg) from 3 days before transplantation were compared at posttransplantation day 3. Echocardiography-derived left ventricular wall thickening was comparable among the 4 groups. Myocardial blood flow assessed with MCE, relating pulsing intervals with signal intensity (SI), was slightly decreased only in untreated allografts. However, myocardial SI (in gray levels) obtained after a 10-minute period allowing microbubble-leukocyte interactions after contrast injection exhibited a clear gradient in these groups (12Ϯ2 in untreated allografts, 9Ϯ5 in allografts treated with low-dose CsA, 6Ϯ3 in allografts treated with high-dose CsA, and 2Ϯ1 in isografts, PϽ0.001). The pattern of difference in SI among the groups agreed well with that in ED-1-positive cell (macrophage) count (25Ϯ7, 12Ϯ4, 5Ϯ3, and 1Ϯ0 cells per high-power field, respectively, PϽ0.001), which correlated with CD3-positive cell (T lymphocyte) count (33Ϯ5, 22Ϯ5, 9Ϯ4, and 1Ϯ0 cells per high-power field, respectively, PϽ0.001). Conclusions-Leukocyte-targeted MCE can noninvasively assess the degree of rejection in transplanted hearts by directly revealing the magnitude of intramyocardial infiltration of macrophages and T lymphocytes.

Noninvasive Contrast-Enhanced Ultrasound Molecular Imaging Detects Myocardial Inflammatory Response in Autoimmune Myocarditis

“…30 Our results are in line with earlier reports that show that CEU molecular imaging can detect cardiac transplant rejection by targeting activated leukocytes or intercellular adhesion molecule-1. 31,32 However, whereas the inflammatory process in transplant rejection shares similarities with myocarditis, an important difference that increases the diagnostic challenges is the low grade and focal nature of the inflammatory infiltrate in moderate myocarditis ( Figure 2B and 2E). Also, the finding that CEU molecular signal for both leukocyte-targeted and P-selectin-targeted MB was greater in severe compared with moderate myocarditis indicates that various degrees of disease activity can be discerned.…”

Microparticle‐ and Nanoparticle‐Based Contrast‐Enhanced Ultrasound Imaging

“…Two studies have been reported to investigate transplant rejection in vivo in animal models. The first study employed passively leukocyte-targeted microbubbles with phosphatidylserine to assess acute allograft rejection in a rat cardiac transplantation model [68]. The degree of rejection in transplanted hearts could be directly revealed by the magnitude of intramyocardial infiltration of macrophages and T lymphocytes due to accumulation of targeted microbubbles at the site of inflammation.…”

Molecular imaging with contrast enhanced ultrasound

“…24 The initial in vivo study demonstrating the ability of CEU to 25 This study demonstrated a 10-fold increase in ICAM-1-targeted microbubble signal compared to control signal and corresponded to grade III to IV rejection on immunohistochemistry in concert with an elevated expression of ICAM-1 (Figure 4). In a similar murine model of acute cardiac rejection, molecular imaging of activated leukocytes was performed using nontargeted microbubbles, 26 thus relying on the nonspecific interactions of activated leukocytes to microbubbles via integrin-and complement-mediated pathways. 3 The degree of CEU signal from activated leukocytes was proportional to the degree of histologic inflammation, rejection grade, and inversely proportional to the degree of immune suppression treatment.…”