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

Lymph nodes (LNs) capture microorganisms that breach the body’s external barriers and enter draining lymphatics, limiting the systemic spread of pathogens1. 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 responses2,3,4. 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 identify SCS macrophages as crucial gatekeepers to the CNS that prevent fatal viral neuroinvasion upon peripheral infection

Conjunctival macrophage-mediated influence of the local and systemic immune response after corneal herpes simplex virus-1 infection

Recently it has been shown that selective subconjunctival macrophage depletion reduced the incidence and severity of stromal herpes simplex virus (HSV) keratitis in mice. In this study, we examined the effect of conjunctival macrophage depletion on the corneal and systemic T-cell-mediated immune response. BALB/c mice were treated with subconjunctival injections of dichloromethylene diphosphonate (Cl(2)MDP)-liposomes (Cl(2)MDP-LIP) or phosphate-buffered saline (PBS) 7 and 2 days before corneal infection with 10(5) plaque-forming units (PFU) of HSV-1 (KOS strain). Interferon (IFN)-γ, interleukin (IL)-2, and IL-4 production in the cornea was analysed by enzyme-linked immunosorbent assay (ELISA), and cytokine mRNA levels (IFN-γ, IL-4) were measured by semiquantitative reverse transcription–polymerase chain reaction (RT-PCR). Cell culture supernatants from submandibular lymph nodes were analysed by ELISA for expression of IFN-γ, IL-2, and IL-4 and by bioassay for IL-6. The HSV-1-specific proliferative response of lymphocytes from regional lymph nodes and the delayed-type hypersensitivity (DTH) response were tested after corneal infection. Virus-neutralizing antibody titres and HSV-1-specific immunoglobulin G (IgG)2a/IgG1-ratios were measured. Cytokine mRNA expression (IFN-γ, IL-4) and secretion (IFN-γ, IL-2, IL-4) in the corneas were decreased after HSV-1 corneal infection in the macrophage-depleted mice. The secretion of IFN-γ and IL-2 was decreased in the regional lymph nodes from Cl(2)MDP-LIP-treated animals (P < 0·05). Furthermore, Cl(2)MDP-LIP-treated mice had decreased HSV-1 specific proliferative responses (P < 0·05) and DTH response after corneal HSV-1 infection (P < 0·05). The virus-neutralizing serum-antibody levels (P < 0·05) increased while the HSV-1 specific IgG2a/IgG1-ratio was unaffected after macrophage depletion. Macrophage depletion did not induce a shift between the T helper 1 (Th1) and Th2 response in this HSK model. The data suggest that conjunctival macrophage functions are enhancing the T-cell-mediated immune response after corneal infection. This effect is at least in part responsible for the impaired course of herpetic keratitis after macrophage depletion

Aging affects AO rat splenic conventional dendritic cell subset composition, cytokine synthesis and T-helper polarizing capacity

It is well-established that almost all cellular components of innate and adaptive immunity undergo age-related remodelling. The findings on age-related changes in both human and mouse dendritic cells (DCs) are conflicting, whereas there are no data on the influence of aging on rat DCs. In an attempt to fill this gap, freshly isolated splenic DCs expressing CD103 (alpha(OX-62) integrin), a DC specific marker recognized by MRC OX62 monoclonal antibody, from 3- (young) and 26-month-old (aged) Albino Oxford rats were examined for subset composition, expression of activation/differentiation markers (CD80, CD86 and CD40 and MHC II molecules) and endocytic capacity using flow cytometric analysis (FCA). In addition, splenic OX62+ DCs cultured in the presence or absence of LPS were analysed for the activation marker and TNF-alpha, IL-6, IL-12, IL-23, TGF-beta 1, IL-10 expression using FCA, RT-PCR and ELISA, respectively. Moreover, the allostimulatory capacity of OX62+ DCs and IFN-gamma, IL-4 and IL-17 production by CD4+ T cells in mixed leukocyte reaction was quantified using FCA and ELISA, respectively. It was found that aging: i) shifts the CD4+:CD4- subset ratio in the OX62+ DCs population towards the CD4- subset and ii) influences DCs maturation (judging by activation marker expression and efficiency of endocytosis) by affecting the expression of intrinsic (TNF-alpha and IL-10) and extrinsic maturation regulators. Furthermore, in LPS-matured OX62+ DCs from aged rats expression of TNF-alpha, IL-12, IL-23 and IL-6 was increased, whereas that of IL-10 was diminished compared with the corresponding cells from young rats. Moreover, in MLR, OX62+ DCs from aged rats exhibited enhanced Th1/Th17 driving force and diminished allostimulatory capacity compared with those from young rats