Blood transcriptome research will also benefi t from concep tual advances that may help address shortcomings inherent to whole blood profi ling. First, blood is a complex tissue and changes in transcript abundance can be attributed to either transcriptional regulation or relative changes in composition of leukocyte populations. Two approaches exist for 'deconvoluting' these two phenomena. First, one can isolate and individually profi le diff erent cell populations present in the blood. Th is approach may also permit the identifi cation of transcripts expressed at low levels or the detection of diff erences in expression that would otherwise be drowned in whole blood [134, 135] . However, isolation methods may introduce technical bias, and require extensive sample processing. A second approach consists of deconvoluting whole blood transcriptional profi les 'in silico' . Th is type of analysis attempts to deduce cellular composition or cell-specifi c levels of gene expression using statistical methodologies [136] [137] [138] [139] [140] [141] .