[Show abstract][Hide abstract] ABSTRACT: Experimental murine herpes simplex virus (HSV)-1 brain infection stimulates microglial cell-driven proinflammatory chemokine production which precedes the presence of brain-infiltrating systemic immune cells. In the present study, we investigated the phenotypes and infiltration kinetics of leukocyte trafficking into HSV-infected murine brains. Using real-time bioluminescence imaging, the infiltration of luciferase-positive splenocytes, transferred via tail vein injection into the brains of HSV-infected animals, was followed over an 18-day time course. Flow cytometric analysis of brain-infiltrating leukocytes at 5, 8, 14, and 30 days postinfection (d.p.i.), was performed to assess their phenotype. A predominantly macrophage (CD45(high)CD11b(+)Ly6C(high)) and neutrophil (CD45(high)CD11b(+)Ly6G(+)) infiltration was seen early during infection, with elevated levels of TNF-alpha mRNA expression. By 14 d.p.i., the phenotypic profile shifted to a predominantly lymphocytic (CD45(high)CD3(+)) infiltrate. This lymphocyte infiltrate was detected until 30 d.p.i., when infectious virus could not be recovered, with CD8(+) and CD4(+) T cells present at a 3:1 ratio, respectively. This T lymphocyte infiltration paralleled increased IFN-gamma mRNA expression in the brain. Activation of resident microglia (CD45(int)CD11b(+)) was also detected until 30 d.p.i., as assessed by MHC class II expression. Activated microglial cells were further identified as the predominant source of IL-1beta. In addition, infected mice given primed immunocytes at 4 d.p.i. showed a significant increase in mortality. Taken together, these results demonstrate that intranasal infection results in early macrophage and neutrophil infiltration into the brain followed by prolonged microglial activation and T lymphocyte retention. Similar prolonged neuroimmune activation may contribute to the neuropathological sequelae observed in herpes encephalitis patients.
Full-text · Article · Dec 2008 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: Although production of reactive nitrogen and reactive oxygen species (RNS and ROS) is a component of innate defense against viral infection, their overproduction in the brain may also lead to deleterious consequences. To investigate potential immunopathologic roles of oxidative stress during herpes encephalitis, the authors examined the expression kinetics of inducible nitric oxide synthase (iNOS) as well as heme oxygenase-1 (HO-1), a marker of oxidative stress, and evaluated infection-induced oxidative brain damage. Results from these studies showed that both iNOS and HO-1 gene expression were highly elevated in the brain within 7 days post infection (d.p.i.) and remained elevated through 21 d.p.i. Real-time bioluminescence imaging of HO-1 promoter-luciferase transgenic mice confirmed HO-1 promoter activity in the brains of HSV-1-infected animals within 3 d.p.i., which peaked between 5 and 7 d.p.i. Immunohistochemical staining for both 3-nitrotyrosine and 8-hydroxydeoxyguanosine (8-OH-dG), as well as quantitative assessment of 8-isoprostane levels, demonstrated the presence of viral infection-induced oxidative brain damage. In addition, when brain leukocytes obtained from animals with experimental herpes encephalitis were sorted using fluorescence-activated cell sorting (FACS) and the individual cell populations analyzed, CD45(int)/CD11b(+) resident microglia were found to be the major cellular source of iNOS expression.
Preview · Article · Jun 2008 · Journal of NeuroVirology
[Show abstract][Hide abstract] ABSTRACT: Central nervous system (CNS) infection with herpes simplex virus (HSV)-1 triggers neuroinflammatory responses leading to peripheral immune cell infiltration into the brain. Previous in vitro studies from our laboratory, using primary human brain cells, implicated microglia as the cellular source of infection-induced chemokines, such as CXC ligand 10 (CXCL10) and CC ligand 2 (CCL2). Here, we evaluated the role of microglial cells in HSV-induced neuroimmune responses using an in vivo murine model of herpes encephalitis. Data obtained during this study demonstrated robust levels of CXCL10, CCL2 and CXCL9 detectable in the brains of infected BALB/c mice between 5 and 8 days post-infection (p.i.). Microglial cells were identified as a source of this HSV-induced chemokine production. Additional experiments established that induction of these immune mediators preceded the presence of CD3, CD4, CD8, and CD45 mRNA in the brain, and immunohistochemical analysis confirmed the presence of infiltrating CD3(+) cells. Further analysis suggested that microglia-derived chemokines drive peripheral immune cell chemotaxis, as antibodies to CXCL10 and CCL2 blocked the migration of murine splenocytes toward HSV-infected microglia by approximately 59.3+/-4.1% and 17.5+/-1.4%, respectively. Taken together, these results demonstrate that a vigorous microglia-driven cascade of pro-inflammatory immune responses is not sufficient to protect susceptible mice from HSV-1 brain infection.
[Show abstract][Hide abstract] ABSTRACT: Infection of the central nervous system (CNS) with herpes simplex virus (HSV)-1 initiates a rapidly progressive, necrotizing, and fatal encephalitis in humans. Even with the advent of antiviral therapy, effective treatments for HSV-1 brain infection are limited because the cause of the resulting neuropathogenesis is not completely understood. We previously reported that human microglial cells, while nonproductively infected, respond to HSV-1 by producing robust amounts of pro-inflammatory mediators, such as tumor necrosis factor(TNF), interleukin (IL)-1beta, CCL5 (RANTES), and CXCL10 (IP-10). Although initiation of immune responses by glial cells is an important protective mechanism in the CNS, unrestrained inflammatory responses may result in irreparable brain damage. To elucidate the potential immunomodulatory role of anti-inflammatory cytokines, we investigated the effects of IL-4, IL-10, and transforming growth factor (TGF)-beta on microglial cell cytokine and chemokine production in response to HSV-1. Results from these studies demonstrated a consistent IL-10-mediated suppression of TNF-alpha (60% +/- 2%), IL-1beta (68% +/- 3%), CCL5 (62 +/- 4%), but not CXCL10 production by HSV-1-infected microglial cells. This inhibition was associated with decreased HSV-1-induced activation of NF-kappaB. These results suggest that IL-10 has the ability to regulate microglial cell production of immune mediators and thereby, dampen the pro-inflammatory response to HSV-1.