Background: Endomyocardial biopsy (EMB) remains the gold standard for acute cellular rejection (ACR) diagnosis in cardiac transplantation yet is subject to interobserver variability. A method that could avoid discordant EMB analysis would be desirable. The apoptosis rate in EMB correlates with ACR severity. Apollon inhibits apoptosis, and RNF41 catalyzes its degradation. Whether tissue Apollon/RNF41 could diagnose ACR is not known. This study addressed this issue.
Methods: Apollon/RNF41 messenger RNA (mRNA) was measured by real time reverse-transcriptase polymerase chain reaction and apoptosis was quantified with TUNEL assays in EMBs of 268 transplant recipients. EMBs were obtained at 1, 2, 3, 4, 7, 12, 24, and 52 posttransplant weeks.
Results: At all time points posttransplant, Apollon mRNA decreased significantly in EMBs with ACR grades 2R/3R combined (P<or=0.0010) compared with 0/1R combined, although RNF41 mRNA significantly increased in EMBs with ACR grade 1R (P<0.0001) or 2R/3R combined (P<0.0001) compared with 0. At the identified cut-off level of less than or equal to 168.2 arbitrary units, Apollon mRNA identified ACR grades 2R/3R with 100% sensitivity and 84% specificity, whereas RNF41 mRNA at the cut-off level of more than or equal to 51.8 identified ACR grades 1R-3R with 99% sensitivity and 95% specificity. Increased RNF41 (rs, 0.728; P<0.0001) and decreased Apollon (rs, -0.562; P<0.0001) expression correlated significantly with the degree of apoptosis in EMBs.
Conclusions: Combined Apollon/RNF41 mRNA quantitatively and specifically identifies ACR associated with apoptosis in cardiac allografts and could validate ACR grading variability associated with histologic EMB analysis.