Human Dendritic Cell Subsets from Spleen and Blood Are Similar in Phenotype and Function but Modified by Donor Health Status

Abstract

Mouse dendritic cells (DC) have been extensively studied in various tissues, especially spleen, and they comprise subsets with distinct developmental origins, surface phenotypes, and functions. Considerably less is known about human DC due to their rarity in blood and inaccessibility of other human tissues. The study of DC in human blood has revealed four subsets distinct in phenotype and function. In this study, we describe four equivalent DC subsets in human spleen obtained from deceased organ donors. We identify three conventional DC subsets characterized by surface expression of CD1b/c, CD141, and CD16, and one plasmacytoid DC subset characterized by CD304 expression. Human DC subsets in spleen were very similar to those in human blood with respect to surface phenotype, TLR and transcription factor expression, capacity to stimulate T cells, cytokine secretion, and cross-presentation of exogenous Ag. However, organ donor health status, in particular treatment with corticosteroid methylprednisolone and brain death, may affect DC phenotype and function. DC T cell stimulatory capacity was reduced but DC were qualitatively unchanged in methylprednisolone-treated deceased organ donor spleen compared with healthy donor blood. Overall, our findings indicate that human blood DC closely resemble human spleen DC. Furthermore, we confirm parallels between human and mouse DC subsets in phenotype and function, but also identify differences in transcription factor and TLR expression as well as functional properties. In particular, the hallmark functions of mouse CD8α+ DC subsets, that is, IL-12p70 secretion and cross-presentation, are not confined to the equivalent human CD141+ DC but are shared by CD1b/c+ and CD16+ DC subsets.

The equivalents of human blood and spleen dendritic cell subtypes can be generated in vitro from human CD34+ stem cells in the presence of fms-like tyrosine kinase 3 ligand and thrombopoietin

“…TLR3 was most highly expressed by CLEC9A 1 cDCs and also at moderate levels by CD1b/c 1 cDCs similar to human blood and spleen DC, although the difference in expression between the CD1b/c 1 DCs and the CLEC9A 1 DCs was more pronounced in blood DC. 24 Similarly, like human blood DCs, TLR7 was expressed most highly by CD123 1 pDCs, and also at moderate levels by the CD1b/c 1 and CLEC9A 1 cDCs as well as the CD14 1 monocytes, albeit the general expression levels were lower. 24 TLR9 was expressed mainly by CD123 1 pDC similar to their in vivo counterparts 24 (Figure 2b).…”

“…24 Similarly, like human blood DCs, TLR7 was expressed most highly by CD123 1 pDCs, and also at moderate levels by the CD1b/c 1 and CLEC9A 1 cDCs as well as the CD14 1 monocytes, albeit the general expression levels were lower. 24 TLR9 was expressed mainly by CD123 1 pDC similar to their in vivo counterparts 24 (Figure 2b). …”

“…21,31,32 The cultured CLEC9A 1 DC also expressed this molecule (Figure 1d). CLEC9A is therefore unique to spleen and blood CD141 1 DCs 16,24 and was thus used as a marker to distinguish this subset in subsequent experiments.…”

“…24 It has recently been shown that blood CD1b/c 1 DCs produce high levels of IL-1b in the presence of Poly(I : C) (PIC), a TLR3 agonist compared to unstimulated controls. 22 Flt3L-derived CD1b/c 1 DCs responded in a similar manner with high levels of IL-1b produced in the presence of PIC but not in its absence (Figure 3b).…”

“…15 Recently, the four populations of human DCs identified in blood have also been found in human spleen with similar phenotype and functions. 24 Human spleen are difficult to obtain and thus, a culture system that is capable of generating the DC subsets in vitro would be of great use for further DC research.…”