Leukocytes have approximately 1,000 times more RNA than platelets or erythrocytes. We also estimated absolute miRNA quantities per hematopoietic cell and per blood volume. As expected, T-cells, B-cells and granulocytes had higher miRNA contents than platelets and erythrocytes, most likely because of the greater size and ongoing transcription in leukocytes. However, compared to nucleated cells, platelets and erythrocytes had a higher fraction of miRNA. Because platelets and erythrocytes have no new RNA synthesis, this difference may simply reflect greater stability of miRNA compared to larger RNAs. There is no reason to expect that platelets and erythrocytes endocytose miRNA to a greater extent than do T-cells, B-cells and granulocytes. The greater contribution of erythrocytes and platelets to blood volume reflects the considerably higher numbers of these cells in blood compared to leukocytes. Considering the relative abundance of LY2109761 microvessicles originating from these cells, erythrocytes, granulocytes and platelets have the potential to have the greatest effect on the systemic effect of miRNA delivery. Numerous miRNAs were identified as DE across cell types. Although we used qRT-PCR to validate selected miRNA expression levels, we cannot exclude platform-specific miRNA differences that might affect our results. Individual miRNAs that were DE by cell type may be useful for identifying the cell of origin of biomarkers or microvessicles and for offering a framework for understanding pathophysiology. In addition, patterns of miRNA expression were highly correlated with cell lineage defined by surface antigens, consistent with work using mRNA profiles from the Orkin laboratory. Future studies are needed to evaluate miRNA profiles as markers of hematologic disease activity and response to treatment, and to assess whether these DE miRNAs are involved in lineage differentiation. Several cell-preferentially expressed miRNAs are worth noting. Nearly half the total erythrocyte miRNA content was represented by miR-451a, a finding consistent with its established critical function in erythroid differentiation and in erythrocyte susceptibility to oxidative stress viamiR-451a-induced repression of 14-3-3j. Similarly, we observed high levels of miR-150 in both T-cell and B-cells, consistent with the role of this miRNA in lymphoid cell differentiation via its regulation of the cMyb transcription factor. Older literature refers to miR-223 as myeloid-specific, but the high level we observed in platelets is consistent with other reports, and high levels were also found in Meg-01 cells that display megakaryocytic properties. We found miR-223 to be the most abundant granulocyte miRNA, consistent with another report using peripheral blood and with the increased expression of miR-223 that occurs during granulocyte differentiation. It is well-accepted that miR223 regulates granulocyte differentiation and function, although the exact molecular mechanism appears complex since ectopic expression of miR-223 in leukemic cells enhanced myeloid differentiation.