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Inflammatory monocytes damage the hippocampus during acute picornavirus infection of the brain.

Howe CL, Lafrance-Corey RG, Sundsbak RS, Lafrance SJ - J Neuroinflammation (2012)

Bottom Line: Identification of the immune effectors responsible for injuring the brain during acute infection is necessary for the development of therapeutic strategies that reduce neuropathology but maintain immune control of the virus.Specific depletion of neutrophils with the 1A8 antibody failed to preserve neurons, suggesting that inflammatory monocytes are the key effectors of brain injury during acute picornavirus infection of the brain.These effector cells may be important therapeutic targets for immunomodulatory or immunosuppressive therapies aimed at reducing or preventing central nervous system pathology associated with acute viral infection.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA. howe@mayo.edu

ABSTRACT

Background: Neuropathology caused by acute viral infection of the brain is associated with the development of persistent neurological deficits. Identification of the immune effectors responsible for injuring the brain during acute infection is necessary for the development of therapeutic strategies that reduce neuropathology but maintain immune control of the virus.

Methods: The identity of brain-infiltrating leukocytes was determined using microscopy and flow cytometry at several acute time points following intracranial infection of mice with the Theiler's murine encephalomyelitis virus. Behavioral consequences of immune cell depletion were assessed by Morris water maze.

Results: Inflammatory monocytes, defined as CD45hiCD11b++F4/80+Gr1+1A8-, and neutrophils, defined as CD45hiCD11b+++F4/80-Gr1+1A8+, were found in the brain at 12 h after infection. Flow cytometry of brain-infiltrating leukocytes collected from LysM: GFP reporter mice confirmed the identification of neutrophils and inflammatory monocytes in the brain. Microscopy of sections from infected LysM:GFP mice showed that infiltrating cells were concentrated in the hippocampal formation. Immunostaining confirmed that neutrophils and inflammatory monocytes were localized to the hippocampal formation at 12 h after infection. Immunodepletion of inflammatory monocytes and neutrophils but not of neutrophils only resulted in preservation of hippocampal neurons. Immunodepletion of inflammatory monocytes also preserved cognitive function as assessed by the Morris water maze.

Conclusions: Neutrophils and inflammatory monocytes rapidly and robustly responded to Theiler's virus infection by infiltrating the brain. Inflammatory monocytes preceded neutrophils, but both cell types were present in the hippocampal formation at a timepoint that is consistent with a role in triggering hippocampal pathology. Depletion of inflammatory monocytes and neutrophils with the Gr1 antibody resulted in hippocampal neuroprotection and preservation of cognitive function. Specific depletion of neutrophils with the 1A8 antibody failed to preserve neurons, suggesting that inflammatory monocytes are the key effectors of brain injury during acute picornavirus infection of the brain. These effector cells may be important therapeutic targets for immunomodulatory or immunosuppressive therapies aimed at reducing or preventing central nervous system pathology associated with acute viral infection.

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Flow cytometric scatter characteristics of brain-infiltrating leukocytes (BILs) from acutely infected mice. BILs collected from Theiler's murine encephalomyelitis virus (TMEV)-infected mice at 18 hpi were gated by forward scatter (FSC) and side scatter (SSC) profiles into three distinct populations (A). Fraction 1 corresponded to the CD45hiCD11b+++1A8+ neutrophil fraction (B). Fraction 2 corresponded to the CD45hiCD11b++Gr1+ inflammatory monocyte population (C). Fraction 3 contained only CD45midCD11b+Gr1-1A8- microglia (resident macrophages) (D). Results are representative of three mice.
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Figure 3: Flow cytometric scatter characteristics of brain-infiltrating leukocytes (BILs) from acutely infected mice. BILs collected from Theiler's murine encephalomyelitis virus (TMEV)-infected mice at 18 hpi were gated by forward scatter (FSC) and side scatter (SSC) profiles into three distinct populations (A). Fraction 1 corresponded to the CD45hiCD11b+++1A8+ neutrophil fraction (B). Fraction 2 corresponded to the CD45hiCD11b++Gr1+ inflammatory monocyte population (C). Fraction 3 contained only CD45midCD11b+Gr1-1A8- microglia (resident macrophages) (D). Results are representative of three mice.

Mentions: In order to corroborate these working definitions, we carefully examined the forward and side scatter profiles of the 18 hpi BILs population from a large number of mice. Gating of the scatter profiles as shown in Figure 3A yielded three distinct cell populations that consistently displayed almost pure populations of neutrophils (fraction 1, Figure 3B), inflammatory monocytes (fraction 2, Figure 3C), or microglia (resident macrophages; CD45midCD11b+Gr1-1A8-) (fraction 3, Figure 3D) using the flow cytometric definitions provided above. Flow sorting to isolate each of these three populations followed by histological examination of the cells further supported our definitions (data not shown) [17,18].


Inflammatory monocytes damage the hippocampus during acute picornavirus infection of the brain.

Howe CL, Lafrance-Corey RG, Sundsbak RS, Lafrance SJ - J Neuroinflammation (2012)

Flow cytometric scatter characteristics of brain-infiltrating leukocytes (BILs) from acutely infected mice. BILs collected from Theiler's murine encephalomyelitis virus (TMEV)-infected mice at 18 hpi were gated by forward scatter (FSC) and side scatter (SSC) profiles into three distinct populations (A). Fraction 1 corresponded to the CD45hiCD11b+++1A8+ neutrophil fraction (B). Fraction 2 corresponded to the CD45hiCD11b++Gr1+ inflammatory monocyte population (C). Fraction 3 contained only CD45midCD11b+Gr1-1A8- microglia (resident macrophages) (D). Results are representative of three mice.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3368782&req=5

Figure 3: Flow cytometric scatter characteristics of brain-infiltrating leukocytes (BILs) from acutely infected mice. BILs collected from Theiler's murine encephalomyelitis virus (TMEV)-infected mice at 18 hpi were gated by forward scatter (FSC) and side scatter (SSC) profiles into three distinct populations (A). Fraction 1 corresponded to the CD45hiCD11b+++1A8+ neutrophil fraction (B). Fraction 2 corresponded to the CD45hiCD11b++Gr1+ inflammatory monocyte population (C). Fraction 3 contained only CD45midCD11b+Gr1-1A8- microglia (resident macrophages) (D). Results are representative of three mice.
Mentions: In order to corroborate these working definitions, we carefully examined the forward and side scatter profiles of the 18 hpi BILs population from a large number of mice. Gating of the scatter profiles as shown in Figure 3A yielded three distinct cell populations that consistently displayed almost pure populations of neutrophils (fraction 1, Figure 3B), inflammatory monocytes (fraction 2, Figure 3C), or microglia (resident macrophages; CD45midCD11b+Gr1-1A8-) (fraction 3, Figure 3D) using the flow cytometric definitions provided above. Flow sorting to isolate each of these three populations followed by histological examination of the cells further supported our definitions (data not shown) [17,18].

Bottom Line: Identification of the immune effectors responsible for injuring the brain during acute infection is necessary for the development of therapeutic strategies that reduce neuropathology but maintain immune control of the virus.Specific depletion of neutrophils with the 1A8 antibody failed to preserve neurons, suggesting that inflammatory monocytes are the key effectors of brain injury during acute picornavirus infection of the brain.These effector cells may be important therapeutic targets for immunomodulatory or immunosuppressive therapies aimed at reducing or preventing central nervous system pathology associated with acute viral infection.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA. howe@mayo.edu

ABSTRACT

Background: Neuropathology caused by acute viral infection of the brain is associated with the development of persistent neurological deficits. Identification of the immune effectors responsible for injuring the brain during acute infection is necessary for the development of therapeutic strategies that reduce neuropathology but maintain immune control of the virus.

Methods: The identity of brain-infiltrating leukocytes was determined using microscopy and flow cytometry at several acute time points following intracranial infection of mice with the Theiler's murine encephalomyelitis virus. Behavioral consequences of immune cell depletion were assessed by Morris water maze.

Results: Inflammatory monocytes, defined as CD45hiCD11b++F4/80+Gr1+1A8-, and neutrophils, defined as CD45hiCD11b+++F4/80-Gr1+1A8+, were found in the brain at 12 h after infection. Flow cytometry of brain-infiltrating leukocytes collected from LysM: GFP reporter mice confirmed the identification of neutrophils and inflammatory monocytes in the brain. Microscopy of sections from infected LysM:GFP mice showed that infiltrating cells were concentrated in the hippocampal formation. Immunostaining confirmed that neutrophils and inflammatory monocytes were localized to the hippocampal formation at 12 h after infection. Immunodepletion of inflammatory monocytes and neutrophils but not of neutrophils only resulted in preservation of hippocampal neurons. Immunodepletion of inflammatory monocytes also preserved cognitive function as assessed by the Morris water maze.

Conclusions: Neutrophils and inflammatory monocytes rapidly and robustly responded to Theiler's virus infection by infiltrating the brain. Inflammatory monocytes preceded neutrophils, but both cell types were present in the hippocampal formation at a timepoint that is consistent with a role in triggering hippocampal pathology. Depletion of inflammatory monocytes and neutrophils with the Gr1 antibody resulted in hippocampal neuroprotection and preservation of cognitive function. Specific depletion of neutrophils with the 1A8 antibody failed to preserve neurons, suggesting that inflammatory monocytes are the key effectors of brain injury during acute picornavirus infection of the brain. These effector cells may be important therapeutic targets for immunomodulatory or immunosuppressive therapies aimed at reducing or preventing central nervous system pathology associated with acute viral infection.

Show MeSH
Related in: MedlinePlus