Blood consists of different cell populations with distinct functions and correspondingly, distinct gene expression profiles. In this study, global miRNA expression profiling was performed across a panel of nine human immune cell subsets (neutrophils, eosinophils, monocytes, B cells, NK cells, CD4 T cells, CD8 T cells, mDCs and pDCs) to identify cell-type specific miRNAs. mRNA expression profiling was performed on the same samples, to determine if miRNAs specific to certain cell types down-regulated expression levels of their target genes.

Nine cell subsets (CD16+CD66b+ Neutrophils, CD16-CD66b+ Eosinophils, CD14+ Monocytes, CD4+ T cells, CD8+ T cells, CD56+ NK cells, CD19+ B cells, CD123+ pDCs and CD11c+ mDCs) were isolated from healthy human blood and assessed for cell type purity by flow cytometry. Cell types were isolated from 5 pools of 5 healthy donors each, with the exception for monocytes, where 10 pools were used. RNA obtained from these purified populations were subsequently used for miRNA and mRNA expression profiling by Affymetrix GeneChip miRNA and HG-U133Plus2.0 microarrays.