Immunohistochemistry staining of C4d to diagnose anti body-mediated rejection in cardiac transplantation

Background: Antibody-mediated rejection (AMR) is associated with poorer outcomes in cardiac transplantation. The clinical diagnosis of AMR has been confirmed by immunofluorescence for C4d on fresh-frozen cardiac tissue. Immunohistochemistry (IHC) has been suggested as a more practical diagnostic tool because it can be performed on routine paraffin-embedded tissue. There are few published data about hemodynamics and C4d staining. We prospectively performed C4d staining on endomyocardial biopsies (EMBs) and present the pattern of tissue staining and its correlation with intracardiac hemodynamics. Methods: EMBs were evaluated by IHC for C4d staining and graded for cellular rejection using ISHLT criteria on hematoxylin-and-eosin-stained sections. Hemodynamic measurements were taken concurrently. Staining for C4d was described as absent, present with serum staining, or present with only tissue staining. The pattern of tissue staining was categorized by location of staining and correlated with intracardiac hemodynamics. Patient demographics, cytomegalovirus status, panel-reactive antibody levels and hemodynamics were analyzed by analysis of variance and chi-square statistics. Results: Of the 400 EMBs, 50 had no C4d staining, 330 had tissue and serum staining, whereas 20 had only tissue staining. Forty EMBs had endothelial staining, including 35 with serum and 5 with isolated tissue staining. Endothelial staining correlated with higher intracardiac pressures. Conclusions: IHC staining for C4d has been suggested for the diagnosis of AMR. Our data suggest there is a high rate of background C4d staining, but endothelial staining correlates with poorer hemodynamics. Methods for IHC staining and interpretation need to be standardized for widespread use and clinical studies.