We read the article by Aguilera et al. 1 and the accompanying editorial by Bellamy 2 with great interest. As Bellamy indicates, our group has documented complement component 4d (C4d) staining in ABO-compatible liver allograft recipients in 2 recent publications. 3,4 There is 1 point in Bellamy's discussion that needs to be corrected: our patients should not be described as having hyperacute rejection but rather should be classified as having acute antibody-mediated rejection (AMR). In our articles, we have been very careful to use the previously established consensus conference definition of AMR for solid organ grafts 5 : graft dysfunction, histological evidence of AMR (as defined by Demetris et al. 6 for liver grafts), donor-specific alloantibodies (DSAs) in the recipient's serum, and strong staining for C4d on endothelial cells. In addition, we feel that our demonstration of C4d in fresh-frozen biopsy samples with the immunofluorescence (IF) technique (the gold standard) gives our reports important additional validity. We attempted to correlate our IF findings from fresh-frozen liver biopsy samples to the immunohistochemistry (IHC) staining of formalin-fixed, paraffin-embedded samples (both at our institution and with the assistance of our colleagues in Basel). We agree with Bellamy and others that it is very challenging to use the IHC technique on formalin-fixed, paraffin-embedded tissue from the liver with its high protein levels; indeed, the liver is much more challenging than other organs (most notably the kidneys). We congratulate Aguilera et al. for detailing the specifics of their IHC protocol, and we strongly encourage them and others who are interested in C4d staining in liver tissue to perform IF and IHC staining in parallel in order to determine whether there is a good correlation between the 2 techniques. As we stated in our previous articles, 3,4 we believe that discussions of liver trans-Address reprint requests to