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

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.

Cell Depletion in Mice That Express Diphtheria Toxin Receptor under the Control of SiglecH Encompasses More Than Plasmacytoid Dendritic Cells

“…We found that SiglecH eGFP/eGFP mice had increased levels of systemic IFN-α compared to WT mice at 48 h p.i. (Figure 2E), similar to a recent study (11). Taken together, these data suggest that SiglecH deficiency does not affect IFN-I secretion by pDC in response to a synthetic TLR9 ligand or virus ex vivo but may influence IFN-I production by pDC during viral infection in vivo.…”

“…Corroborating these findings, SiglecH eGFP/eGFP mice also had slightly elevated levels of systemic IFN-α and proinflammatory cytokines compared to WT mice after HSV-1 infection (Figure 3A–C). These results are consistent with an immunomodulatory role for SiglecH in antiviral responses (6, 9, 11). To determine whether this effect was due to pDC, we bred CLEC4C-DTR Tg mice to SiglecH eGFP/+ and SiglecH eGFP/eGFP mice and infected them with HSV-1 in the presence or absence of pDC.…”

“…Our previous work has shown that pDC numbers are reduced in spleens of infected mice, which appeared to be a consequence of cell death (17). A recent study has indicated that following stimulation with CpGA or infection with MCMV that SiglecH is downregulated in a TLR9/MyD88-dependent manner (11). To determine if reduced pDC numbers during infection are due to reduced detection of SiglecH expression, we compared SiglecH and eGFP expression in pDC from spleens of SiglecH eGFP/+ mice infected or not with HSV-1.…”

“…It has been shown that SiglecH has an immunomodulatory role during inflammation and viral infections (6, 9, 11). To determine whether SiglecH deficiency altered cytokine production by pDC, we measured IFN-α levels in supernatants from enriched or sort-purified pDC from WT and SiglecH eGFP/eGFP mice stimulated ex vivo with CpGA.…”

“…SiglecH DTR/DTR mice lack SiglecH expression and can be depleted of pDC with DT. SiglecH is a member of the sialic acid-binding immunoglobulin-like lectin family that is commonly used to discriminate pDC from other cell types in mice and appears to have an immunomodulatory role during viral infections (6, 9–11). Because the results and conclusions obtained from these two inducible pDC depletion models differ in magnitude, it is important to investigate reasons for discrepancies.…”