White Blood Cell Differentials Enrich Whole Blood Expression Data in the Context of Acute Cardiac Allograft Rejection

Acute cardiac allograft rejection is a serious complication of heart transplantation. Investigating molecular processes in whole blood via microarrays is a promising avenue of research in transplantation, particularly due to the non-invasive nature of blood sampling. However, whole blood is a complex tissue and the consequent heterogeneity in composition amongst samples is ignored in traditional microarray analysis. This complicates the biological interpretation of microarray data. Here we have applied a statistical deconvolution approach, cell-specific significance analysis of microarrays (csSAM), to whole blood samples from subjects either undergoing acute heart allograft rejection (AR) or not (NR). We identified eight differentially expressed probe-sets significantly correlated to monocytes (mapping to 6 genes, all down-regulated in ARs versus NRs) at a false discovery rate (FDR) <= 15%. None of the genes identified are present in a biomarker panel of acute heart rejection previously published by our group and discovered in the same data. A single treatable acute rejection (International Society for Heart & Lung Transplantation, ISHLT grade >=2R) sample from each of 10 subjects and one non-rejection sample (ISHLT grade = 0R) from 16 subjects who did not have treatable acute rejection at any time within the first six months post-transplant were selected for analysis. Groups had similar mean age (48 ± 14 and 50 ± 16 in ARs and NRs, respectively) and were mainly composed of Caucasian subjects. NRs were more predominantly male (14/16 subjects) compared to ARs (6/10 subjects).