Immune Cell Profiling of IFN-λ Response Shows pDCs Express Highest Level of IFN-λR1 and Are Directly Responsive via the JAK-STAT Pathway

Abstract

The interferon lambda (IFN-l) cytokines have well-known antiviral properties, yet their contribution to immune regulation is not well understood. Epithelial cells represent the major target cell of IFN-l; peripheral blood mononuclear cells are generally considered nonresponsive, with the exception of plasmacytoid dendritic cells (pDCs). In this study we aimed to define the potential for discrete subpopulations of cells to directly respond to IFN-l. Analysis of peripheral blood leukocytes reveals that, while pDCs uniformly express the highest levels of IFN-l receptor, a small proportion of B cells and monocytes also express the receptor. Nevertheless, B cells and monocytes respond poorly to IFN-l stimulation in vitro, with minimal STAT phosphorylation and interferonstimulated gene (ISG) induction observed. We confirm that pDCs respond to IFN-l in vitro, upregulating their expression of pSTAT1, pSTAT3, and pSTAT5. However, we found that pDCs do not upregulate pSTAT6 in response to IFN-l treatment. Our results highlight unique aspects of the response to IFN-l and confirm that while the IFN-l receptor is expressed by a small proportion of several different circulating immune cell lineages, under normal conditions only pDCs respond to IFN-l stimulation with robust STAT phosphorylation and ISG induction. The difference in STAT6 responsiveness of pDCs to type I and type III interferons may help explain the divergence in their biological activities.

Contribution of type III interferons to antiviral immunity: location, location, location

“…It has been particularly challenging to define immune cell subsets sensitive to type III IFNs due to the lack of verified research reagents, and the fact that the assessment of levels of transcriptional or protein expression of IFN-R1 does not equate to responsiveness of the cells to IFNs. As an example, B cells may express IFN-R1 but are barely responsive to IFN-s (14,85). NK cells, which are important mediators of anti-tumor activities of both type I and type III IFNs (86 -88), are sensitive to type I IFNs, but whether IFN-s can directly affect NK functions is controversial (86 -90).…”

Interferon-Lambda: A Potent Regulator of Intestinal Viral Infections

“…In the intestine, IFNLR1 is expressed preferentially on IECs, allowing for a compartmentalized response to viruses infecting at this mucosal surface (24,25). While IFNLR1 expression has also been reported on NK cells, T cells, B cells, and pDCs (26)(27)(28)(29)(30), no role has been found for these cells in IFN-λ-mediated antiviral responses. Type I IFNs, on the other hand, are critical for preventing a virus from moving past this initial epithelial barrier into systemic tissues (24,25,31).…”

Interferon-λs and Plasmacytoid Dendritic Cells: A Close Relationship

“…Among human leukocytes, only pDCs and, less prominently, B cells, have been shown to constitutively express a complete IFNλR ( 26 , 27 ). Consistently, IFNλs have been shown to trigger phosphorylation of STAT1 ( 27 , 54 , 55 ), STAT2 ( 54 ), STAT3, and STAT5 ( 55 ), in either freshly isolated pDCs ( 54 ) or pDCs gated among total PBMCs ( 27 , 55 ), as well as various functional responses herein summarized.…”

“…It should be also pointed out that, in a previous study, the levels of MX1 mRNA induced by IFNα in purified pDCs were found to be higher than those induced by IFNλ3 ( 60 ), but IFNα was used at concentrations approximately 10-fold higher than IFNλ3 (1,000 vs 100 IU/ml, respectively). Under similar experimental conditions, only IFNα, but not IFNλs, was shown to activate STAT6 phosphorylation in purified pDCs ( 55 ), independently from the concentrations used.…”

“…For example, 2’-5’-oligoadenylate synthetase 1 (OAS1) and IRF7 mRNAs were found as induced in murine pDCs incubated with 100 ng/ml IFNλ2 ( 52 ). In humans, we and others have reported that both IFNλ1 and IFNλ3 induce the mRNA expression of MX dynamin like GTPase 1 (MX1) ( 59 , 60 ), protein kinase R (PKR), interferon induced protein with tetratricopeptide repeats 1 (IFIT1), ISG ubiquitin-like modifier (ISG15), and C-X-C motif chemokine ligand 10 (CXCL10) ( 54 , 55 , 59 ). Our unpublished observations prove that also CXCL9, TLR7, IFIT2, and TNF-related apoptosis inducing ligand (TRAIL) are induced by IFNλ3 in human pDCs.…”