Echocardiography-guided assessment of mouse cardiac transplant rejection improves model reproducibility.

Background: The mouse heterotopic heart transplant model is a widely used system for dissecting mechanisms of graft rejection and identifying new therapeutic targets, owing to its relative technical simplicity and the availability of well-defined inbred strains. One limitation of the model is that monitoring of the non-life sustaining implanted graft by manual palpation does not provide information regarding the magnitude of the anti-donor immune response and is operator-dependent. Building on previous studies suggesting that trans-abdominal ultrasonography can detect graft rejection more precisely than manual palpation, we tested if changes in motion mode (M-mode) ultrasound also correlated with the magnitude of the anti-donor T cell response. Methods: We performed sets of MHC-mismatched heterotopic heart transplants in mice and quantified the accuracy of palpation vs. ultrasonography in determining graft rejection. In an additional set of mice, we performed mixed lymphocyte reactions to quantify anti-donor T cell immunity at a fixed time point (usual experimental design) or at time points determined by changes in allograft M-mode analysis. Conclusions: The data demonstrate that ultrasonography is superior to manual palpation for determining graft rejection and newly shows that changes in M-mode associate with the magnitude of anti-donor T cell immunity. These findings are important to increase reproducibility and translational impact of studies using this model.