Subcapsular sinus macrophages prevent CNS invasion on peripheral infection with a neurotropic virus

Abstract

Lymph nodes (LNs) capture microorganisms that breach the body's external barriers and enter draining lymphatics, limiting the systemic spread of pathogens 1 . Recent work has shown that CD11b + CD169 + macrophages, which populate the subcapsular sinus (SCS) of LNs, are critical for clearance of viruses from the lymph and for initiating antiviral humoral immune responses 2 , 3 , 4 . Using vesicular stomatitis virus (VSV), a relative of rabies virus transmitted by insect bites, we show here that SCS macrophages perform a third vital function: they prevent lymph-borne neurotropic viruses from infecting the CNS. Upon local depletion of LN macrophages, ~60% of mice developed ascending paralysis and died 7-10 days after subcutaneous infection with a small dose of VSV, while macrophage-sufficient animals remained asymptomatic and cleared the virus. VSV gained access to the nervous system via peripheral nerves in macrophage-depleted LNs. In contrast, within macrophage-sufficient LNs VSV replicated preferentially within SCS macrophages but not in adjacent nerves. Removal of SCS macrophages did not compromise adaptive immune responses against VSV, but reduced type I interferon (IFN-I) production within infected LNs. VSV-infected macrophages recruited IFN-I producing plasmacytoid dendritic cells to the SCS and additionally were a major source of IFN-I themselves. Experiments in bone marrow chimeric mice revealed that IFN-I must act on both hematopoietic and stromal compartments, including the intranodal nerves, to prevent lethal VSV infection. These results Users may view, print, copy, download and text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use: http://www.nature.com/authors/editorial_policies/license.html#terms To explore how neurotropic viruses spread from their entry site to the CNS, we studied VSV, an arthropod-borne rhabdovirus that causes fatal paralytic disease in mammals, including mice 5 . While numerous studies have investigated immune responses to intravenous VSV infection 6 , the immunological consequences elicited by the more natural subcutaneous (sc) route are incompletely understood. Previous work has shown that, following peripheral inoculation, VSV is captured by macrophages in draining LNs, preventing hematogenous dissemination 2 . Here, we asked whether this macrophage filter affects the ability of neurotropic viruses to access the CNS.C57BL/6 mice were injected sc with clodronate liposomes (CLL) into one hind footpad, which selectively eliminated CD11b + CD169 + macrophages in the draining popliteal LN, but not in distal LNs or the spleen 2 . Six days later, mice were challenged in the ipsilateral or contralateral footpad using a low dose (10 4 pfu) of VSV-Indiana. While this dose was cleared by virtually all untreated and contralaterally-infected mice, ~60% of CLL-treated ipsilaterally-infected animals developed ascending CNS pathology starting with ipsilateral hindleg paralysis and progressing to death 7-10 ...

The brain parenchyma has a type I interferon response that can limit virus spread

“…The observation of paracrine IRF7 induction is interesting because the CNS has been reported to not contain cells with high constitutive IRF7 expression (8). In contrast, in the periphery, plasmacytoid dendritic cells express constitutively high IRF7 levels and, together with lymph node macrophages, produce the majority of type I IFN following VSV infection (13). Analogously, in the brain, it is possible that a rapid IRF7 response is necessary to prime cells for a full type I IFN response upon virus spread from infected cells.…”

“…VSV is the prototypic nonsegmented negative-strand RNA virus and has been used extensively to study the systemic innate immune response, which promotes its rapid clearance (13,14). VSV was selected because it has a characteristic transsynaptic anterograde transmission pattern among neurons and is straightforward to track, as it can be engineered to express eGFP (15).…”

α1β1 Integrin-Mediated Adhesion Inhibits Macrophage Exit from a Peripheral Inflammatory Lesion

“…Cell suspensions from digested footpads and draining popliteal LNs were stained for multiple cell-surface markers and analyzed by flow cytometry. A combination of markers including the GR-1 Ab, CD11b, and side-scatter signal allowed us to identify specific myeloid subsets (20) (Fig. 1B).…”

Conventional but Not Plasmacytoid Dendritic Cells Foster the Systemic Virus–Induced Type I IFN Response Needed for Efficient CD8 T Cell Priming

“…5C, 5D). This property is commonly used to discern the role of cDCs and/or macrophages in different biological process using CD11c-DTR mice (37,38). As depicted in Fig.…”