Human 6-Sulfo LacNAc-Expressing Dendritic Cells Are Principal Producers of Early Interleukin-12 and Are Controlled by Erythrocytes

Abstract

Early and high-level production of IL-12 is crucial for effective immune responses against pathogens. Up until now, the cells providing this initial IL-12 have remained elusive. Here we show that a subset of human blood dendritic cells (DC) is the principal and primary source of IL-12p70 when blood leukocytes are stimulated with the TLR4-ligand LPS or with CD40-ligand. These so-called slanDC are characterized by the 6-sulfo LacNAc modification of PSGL-1, which is identified by the mAb M-DC8. The IL-12 response of slanDC requires a few hours of in vitro maturation, which is completely blocked in the presence of erythrocytes. This inhibition of maturation depends on the expression of CD47 on erythrocytes and of its ligand SIRPalpha on DC. While strictly controlled in the blood by erythrocytes, the high IL-12- and TNF-alpha-producing capacity of slanDC in tissues may be critical in fighting off pathogens; if uncontrolled, it may lead to adverse inflammatory reactions.

Semimature Stage: A Checkpoint in a Dendritic Cell Maturation Program That Allows for Functional Reversion after Signal-Regulatory Protein-α Ligation and Maturation Signals

“…Which cell type expressing CD47 precisely interacts with SIRP-␣ on DC and under which conditions does it happen in vivo? Schakel et al (50) recently demonstrated that IL-12 p70 secretion is abundantly secreted in response to TLR ligands by a blood DC subset provided the contact between CD47 on erythrocytes and SIRP-␣ on DC is interrupted. Also, SIRP-␣ is engaged by CD47-expressing live but not apoptotic cells (25).…”

slanDCs selectively accumulate in carcinoma-draining lymph nodes and marginate metastatic cells

“…12). Functionally, slanDCs stand out for their remarkable capacity to produce tumour necrosis factor alpha (TNFa) and IL-12p70 upon stimulation with discrete toll-like receptor ligands 13,14 . In addition, they are potent inducers of primary antigen-specific T-cell responses in vitro 11 , and show a superior programming of Th1/Th17 cell polarization as compared with classical CD1c þ DCs 14 .…”

Acute myeloid leukemia cells fail to activate native human dendritic cells: a potential mechanism of immune evasion

“…Recently, we defined 6-sulfo LacNAc (slan)DCs (formerly termed M-DC8 þ DCs) as a major subpopulation of proinflammatory myeloid human blood DCs, which mainly differ from other blood DC subsets by their selective phenotype (6- 5,6 Functional data revealed that slanDCs can mediate tumor-directed cytotoxicity and efficiently activate tumor-reactive NK cells and CD8 þ CTLs. 7 To get novel insights into the impact of primary human AML cells on native human DCs, we investigated the capacity of AML cells to modulate the secretion of TNF-a and IL-12 by slanDCs.…”

“…5,7 In addition, we have shown that activated slanDCs are principal producers of IL-12, which favors the differentiation of naive CD4 þ T cells into Th1 cells and is important in NK cell activation. 6,8 Blood samples were obtained from healthy donors with informed consent. Immunomagnetic isolation of slanDCs (purity: 490%) from peripheral blood mononuclear cells was performed as previously described.…”

“…Immunomagnetic isolation of slanDCs (purity: 490%) from peripheral blood mononuclear cells was performed as previously described. 6 Primary AML cells were obtained from the bone marrow of patients who had been included into two consecutive multicenter trials (SHG96 and DSIL2003) after informed consent and approval by the institutional review board. The AML samples used for the experiments were classified according to French-AmericanBritish subtypes and percentages of myeloblasts: AML1 (M1, 95%), AML2 (M1, 93,5%), AML3 (M1, 93,5%), AML4 (M1, 92%), AML5 (M1, 92,5%), AML6 (M1, 91,5%), AML7 (M1, 90,5%), AML8 (M5a, 92%), AML9 (M5a, 91,5%), AML10 (M5a, 92,5%), AML11 (M5a, 95%).…”