Comparative analysis of IRF and IFN-alpha expression in human plasmacytoid and monocyte-derived dendritic cells

Abstract

Plasmacytoid dendritic cells (PDC) produce high levels of type I IFN upon stimulation with viruses, while monocytes and monocyte-derived dendritic cells (MDDC) produce significantly lower levels. To find what determines the high production of type I IFN in PDC, we examined the relative levels of IRF transcription factors, some of which play critical roles in the induction of IFN. Furthermore, to determine whether the differences could result from expression of distinct IFNA subtypes, the profile of IFNA genes expressed was examined. PDC responded equally well to stimulation with HSV-1 and Sendai virus (SV) by producing high levels of type I IFN, whereas the MDDC and monocyte response to SV were lower, and neither responded well to HSV-1. All three populations constitutively expressed most of the IRF genes. However, real-time RT-PCR demonstrated increased levels of IRF-7 transcripts in PDC compared with monocytes. As determined by intracellular flow cytometry, the PDC constitutively expressed significantly higher levels of IRF-7 protein than the other populations while IRF-3 levels were similar among populations. Analysis of the profile of IFNA genes expressed in virus-stimulated PDC, monocytes and MDDC demonstrated that each population expressed IFNA1 as the major subtype but that the range of the subtypes expressed in PDC was broader, with some donor and stimulus-dependent variability. We conclude that PDC but not MDDC are uniquely preprogrammed to respond rapidly and effectively to a range of viral pathogens with high levels of IFN-alpha production due to the high levels of constitutively expressed IRF-7.

Development of human plasmacytoid dendritic cells depends on the combined action of the basic helix‐loop‐helix factor E2‐2 and the Ets factor Spi‐B

“…Here we describe that E2-2 and Spi-B cooperate in pDC development. Of notice, both IRF-4 and IRF-8 are highly expressed in human pDC ( [42,51,52], and H. Schmidlin and B. Blom, unpublished results) and crucially involved in murine pDC development [14,16]. It is therefore tempting to speculate that Spi-B, in addition to contributing to the downregulation of Id2 expression, may in complex with E2-2 and IRF-4 and/or IRF-8 bind to a juxtaposed E-box and EICE to promote pDC development.…”

TLR signalling and activation of IRFs: revisiting old friends from the NF-κB pathway

“…Because the induction of type I IFNs is crucially dependent on the activation of IRFs, this raises the intriguing question of how these TLRs can activate IRFs without the help of TRIF. Plasmacytoid DCs show high levels of constitutive IRF7 expression, relative to monocyte-derived DCs [53], and two concomitant reports showed that Myd88 forms a complex with IRF7 to trigger its activation and induce IFN-a [54,55]. TLR7 and TLR9 are located primarily in the intracellular endosomal compartment [56,57] and the Myd88-IRF7 interaction takes place in the endosomal vesicles of the plasmacytoid DCs [58] (Figure 2).…”

A compass that points to lupus: genetic studies on type I interferon pathway

“…ISREs are found in the promoters of various IFN signature genes such as IFNa, IFNb, IL-12, CXCL10 and IFIT1. 68 Expression of IRF5 was detected in B cells and DCs 69 and further enhanced by activation of type I IFN pathway because promoter of IRF5 itself also possesses ISRE. 70 Among the IRF family members, IRF5 and IRF7 are known to share the same signaling pathway that is initiated through TLR7/8 and TLR9.…”