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It's What's on the Inside That Counts for Newly Identified Human Blood Cells!

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Review of “Single-cell RNA-seq reveals new types of human blood dendritic cells, monocytes, and progenitors” from Science by Stuart P. Atkinson

The description of hematopoietic immune cells classically employs a combination of physical features such as cell size, cell shape, and the expression of markers exposed on the cell surface. However, researchers from the laboratories of Muzlifah Haniffa, Aviv Regev, and Nir Hacohen sought to do away with this “shallow” analysis because, as we all know, it’s what's on the inside that counts! 

Specifically, Villani and Satija et al. have employed unbiased single-cell RNA sequencing (RNA-seq) [1] of cells isolated from a drop of human blood to define a new “atlas” of human blood dendritic cells (DCs) and monocytes. The authors hope that their new findings, published in Science, will permit enhanced functional and developmental analyses, improve immune monitoring, provide new therapeutic targets, and act as a starting point for deeper analysis of other human immune cells [2].

The various DCs and monocytes in our blood mediate pathogen sensing, phagocytosis, and antigen presentation [3-5] and RNA analysis of around 2400 lineage-negative HLA-DR-positive cells from human blood revealed a new taxonomy of these cells: six DC and four monocyte populations. The new cell types identified included two additional monocyte populations (one expressing monocyte and cytotoxic genes and another of unknown function) and a new DC progenitor cell that may allow the generation of DCs in vitro. Additionally, the identification of two new DCs that potently activate T cells may enable a deeper understanding of the role that these cells play in tissues, inflammation, and disease. 

This new atlas of human blood DCs and monocytes is now ready for exploration; however, the authors do suggest that there may be even more cell types that remain undiscovered. Furthermore, the team behind this excellent new study also aims to ascertain the particular location of these cell types within lymphoid and non-lymphoid tissues and to apply their strategy to other human immune cells.

Until these new results reach us here at the Stem Cells Portal, just remember that this study provides more evidence that it’s not what we show on the (cell!) surface, it’s what’s on the inside (RNA!) that truly counts!

References

  1. Grun D and van Oudenaarden A. Design and Analysis of Single-Cell Sequencing Experiments. Cell 2015;163:799-810.
  2. Villani AC, Satija R, Reynolds G, et al. Single-cell RNA-seq reveals new types of human blood dendritic cells, monocytes, and progenitors. Science 2017;356:
  3. Mildner A and Jung S. Development and function of dendritic cell subsets. Immunity 2014;40:642-656.
  4. Haniffa M, Bigley V, and Collin M. Human mononuclear phagocyte system reunited. Semin Cell Dev Biol 2015;41:59-69.
  5. Schraml BU and Reis e Sousa C. Defining dendritic cells. Current opinion in immunology 2015;32:13-20.