Absence of Siglec-H in MCMV Infection Elevates Interferon Alpha Production but Does Not Enhance Viral Clearance

Franz Puttur,Heike Schmitt,Bart N Lambrecht,Maxine Swallow,Christian Thomas Mayer,Lars Nitschke,Melanie Gohmert,Roland Lang,Catharina Arnold-Schrauf,Gulhas Solmaz,Marc Lindenberg,Katharina Lahl,Christopher Van Helt,Martin Messerle,Tim Sparwasser

doi:10.1371/journal.ppat.1003648

Abstract

Plasmacytoid dendritic cells (pDCs) express the I-type lectin receptor Siglec-H and produce interferon α (IFNα), a critical anti-viral cytokine during the acute phase of murine cytomegalovirus (MCMV) infection. The ligands and biological functions of Siglec-H still remain incompletely defined in vivo. Thus, we generated a novel bacterial artificial chromosome (BAC)-transgenic “pDCre” mouse which expresses Cre recombinase under the control of the Siglec-H promoter. By crossing these mice with a Rosa26 reporter strain, a representative fraction of Siglec-H+ pDCs is terminally labeled with red fluorescent protein (RFP). Interestingly, systemic MCMV infection of these mice causes the downregulation of Siglec-H surface expression. This decline occurs in a TLR9- and MyD88-dependent manner. To elucidate the functional role of Siglec-H during MCMV infection, we utilized a novel Siglec-H deficient mouse strain. In the absence of Siglec-H, the low infection rate of pDCs with MCMV remained unchanged, and pDC activation was still intact. Strikingly, Siglec-H deficiency induced a significant increase in serum IFNα levels following systemic MCMV infection. Although Siglec-H modulates anti-viral IFNα production, the control of viral replication was unchanged in vivo. The novel mouse models will be valuable to shed further light on pDC biology in future studies.

Highlights

Dendritic cells (DCs) are a diverse population of professional antigen-presenting cells that exhibit differences in both their developmental origins and their functional properties
Swiecki et al demonstrated that specific Plasmacytoid dendritic cells (pDCs) depletion in blood dendritic cell antigen 2 (BDCA2)diphtheria toxin receptor (DTR) transgenic mice at 36 h post infection (p.i.) resulted in impaired murine cytomegalovirus (MCMV) clearance with unhindered NK cell expansion and function at later timepoints during infection [13]
In an additional experimental system, in which pDCs lack Siglec-H function, we demonstrate that this molecule is not important for the regulation of MCMV pathogenicity

Summary

Introduction

Dendritic cells (DCs) are a diverse population of professional antigen-presenting cells that exhibit differences in both their developmental origins and their functional properties. Two prominent murine DC sub-classes exist, conventional DCs (cDCs) and plasmacytoid DCs (pDCs) The latter subset of DCs expresses the I-type lectin receptor Siglec-H. Double stranded DNA viruses like cytomegalovirus (CMV) are sensed by pDCs via the endosomal Toll-like receptor 9 (TLR9) [11] and trigger strong IFNa responses which are critically required for early viral control during MCMV infection [12,13]. To this end, Zucchini et al have shown that pDCs are the main early source of intracellular IFNa/b at 30–36 h post MCMV infection [14]. The precise receptors contributing to pDCmediated anti-viral defence remain incompletely defined

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Conclusion