Dendritic cells are mononuclear cells that are an invaluable part of the immune response. These are antigen presenting cells that process invading pathogens (disease-causing material) and present them to T cells for further response. Different dendritic cell subtypes have been and continue to be identified with varying functions. Nonetheless, the total number of dendritic cell subtypes and the interrelationships between them are unknown.
The traditional approach to identify the different subtypes of dendritic cells is by the use of a limited set of special molecular markers, morphology, function, and their precursors. A new approach using RNA-sequencing (RNA-seq) with single-cell resolution has been employed to more extensively analyze and find new subtypes of dendritic cells and monocytes. RNA-seq is a means to sequence a cell’s total RNA, a reflection of the complete repertoire of gene expression (transcriptome), using the massive-parallel high-throughput sequencing approach, next-generation sequencing.
The sequence information obtained was used to categorize cells into specific groups or clusters. The researchers then identified new markers for each cell cluster. Once having these new markers, they were able to use those to isolate cells that potentially represented newly discovered dendritic cell subtypes. The new markers were then used to determine if the cell types represented by the new markers could be found in the blood of different volunteers. Monocyte subsets were also analyzed in this manner. The expression of genes associated with dendritic cell progenitors and development were also identified and studied.
Once identifying novel dendritic cell subtypes, their functions were studied by measuring the production of various cytokines using a laboratory cytokine detection kit. Using the same new markers, cells were isolated and cultured with T cells to see if the supposed new dendritic cell subtypes could activate the T cells. Based on the study results, there are now six main dendritic cell subtypes consisting of those that are cross-presenting, those characterized by unique markers, and those that are interferon producing. A novel dendritic cell progenitor and four monocyte subtypes were also identified. This new taxonomic approach can lead to enhanced immunologic monitoring of disease states and use in developing new immunotherapies.
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Villani, A., Satija, R., Reynolds, G., Sarkizova, S., Shekhar, K., & Fletcher, J. et al. (2017). Single-cell RNA-seq reveals new types of human blood dendritic cells, monocytes, and progenitors. Science, 356(6335), eaah4573. doi:10.1126/science.aah4573