Leukocyte-targeted myocardial contrast echocardiography can assess the degree of acute allograft rejection in a rat cardiac transplantation model

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(-1) . d(-1)) or high dose (10 mg . kg(-1) . d(-1)) 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 ( 12 +/- 2 in untreated allografts, 9 +/- 5 in allografts treated with low- dose CsA, 6 +/- 3 in allografts treated with high- dose CsA, and 2 +/- 1 in isografts, P < 0.001). The pattern of difference in SI among the groups agreed well with that in ED- 1 - positive cell ( macrophage) count ( 25 +/- 7, 12 +/- 4, 5 +/- 3, and 1 +/- 0 cells per high- power field, respectively, P < 0.001), which correlated with CD3- positive cell ( T lymphocyte) count ( 33 +/- 5, 22 +/- 5, 9 +/- 4, and 1 +/- 0 cells per high- power field, respectively, P < 0.001). 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.