A Fluorescence Reporter Model Defines “Tip-DCs” as the Cellular Source of Interferon β in Murine Listeriosis

Abstract

Production of type I interferons, consisting mainly of multiple IFNα subtypes and IFNβ, represents an essential part of the innate immune defense against invading pathogens. While in most situations, namely viral infections, this class of cytokines is indispensable for host survival they mediate a detrimental effect during infection with L. monocytogenes by rendering macrophages insensitive towards IFNγ signalling which leads to a lethal bacterial pathology in mice. Due to a lack of suitable analytic tools the precise identity of the cell population responsible for type I IFN production remains ill-defined and so far these cells have been described to be macrophages. As in general IFNβ is the first type I interferon to be produced, we took advantage of an IFNβ fluorescence reporter-knockin mouse model in which YFP is expressed from a bicistronic mRNA linked by an IRES to the endogenous ifnb mRNA to assess the IFNβ production on a single cell level in situ. Our results showed highest frequencies and absolute numbers of IFNβ+ cells in the spleen 24 h after infection with L. monocytogenes where they were located predominately in the white pulp within the foci of infection. Detailed FACS surface marker analyses, intracellular cytokine stainings and T cell proliferation assays revealed that the IFNβ+ cells were a phenotypically and functionally further specialized subpopulation of TNF and iNOS producing DCs (Tip-DCs) which are known to be essential for the early containment of L. monocytogenes infection. We proved that the IFNβ+ cells exhibited the hallmark characteristics of Tip-DCs as they produced iNOS and TNF and possessed T cell priming abilities. These results point to a yet unappreciated ambiguous role for a multi-effector, IFNβ producing subpopulation of Tip-DCs in controlling the balance between containment of L. monocytogenes infection and effects detrimental to the host driven by IFNβ.

The C5a Anaphylatoxin Receptor (C5aR1) Protects against Listeria monocytogenes Infection by Inhibiting Type 1 IFN Expression

“…6A). As in prior reports, serum IFN-β levels were quite low (40, 42). However, a consistent difference was seen between WT and C5aR1−/− mice.…”

“…There are two major types of type 1 IFN, IFN-α and IFN-β. In L. monocytogenes models IFN-α expression is partially dependent on IFN-β, and type 1 IFN expression peaks at 24 h (38–40). At this time point both IFN-α and IFN-β were significantly elevated in the serum of C5aR1−/− mice (p ≤ 0.0004) (Fig.…”

CD81 Controls Immunity to Listeria Infection through Rac-Dependent Inhibition of Proinflammatory Mediator Release and Activation of Cytotoxic T Cells

“…The main mechanism described to this harmful role relies on the induction of apoptosis, particularly of lymphocytes as well as macrophages (47,48). It has been shown, using IFN-b reporter mice, that Tip-DCs are an important source of IFN-b during Listeria infection (49) as are CD11b + DCs (50). This finding might suggest that type I IFN production can act as a mechanism of selfregulation by immune cells, which could be subverted by Listeria for its own profit.…”

Independent of Plasmacytoid Dendritic Cell (pDC) infection, pDC Triggered by Virus-Infected Cells Mount Enhanced Type I IFN Responses of Different Composition as Opposed to pDC Stimulated with Free Virus

“…We found that stimulation of pDC with infected cells resulted in another distribution of IFN-a6 + , IFN-b + , and IFN-a6 + IFN-b + cell subsets than observed after stimulation with free virus. Previously, IFN-b + cells were phenotypically described as a specialized subpopulation of TNF and inducible NO synthase-producing DCs (41). It will be a matter of future research to determine markers that qualify subsets of pDC and mDC to respond to virus stimulation and to mount IFN responses.…”