TNF-alpha in acute cardiac transplant rejection

Acute cardiac allograft rejection is an immune-mediated response, hallmarked by cellular infiltration and myocyte damage in the transplanted heart. Cardiac biopsy sampling has been the 'gold' standard for routinely monitoring episodes of acute rejection. As cardiac biopsy is invasive, attention has focused on other non-invasive methods, such as serum analysis, for monitoring purposes. Tumour necrosis factor alpha (TNF-alpha) is a lymphocyte- and macrophage-derived cytokine that is pleiotropic in its actions. Its proinflammatory functions suggest that it may play an important role in initiating and orchestrating the rejection response. Studies demonstrating a correlation in the expression of TNF-alpha with the severity of the rejection episode have placed TNF-alpha as a prime candidate marker of rejection, and have prompted further study to elucidate these findings. This review discusses the limitations of the methodologies used to identify TNF-alpha, and how intragraft expression of TNF-alpha is not reflected in the serum. Furthermore, we describe how other stimuli besides the rejection response can affect TNF-alpha production, arguing against its use as a 'rejection-specific' marker. Nevertheless, genetic studies suggest that TNF-alpha may influence transplant outcome, and offer a new tool for studying the role of TNF-alpha in acute transplant rejection