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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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Visualization of the timecourse of neutrophil and inflammatory monocyte infiltration during acute infection. Uninfected mice (A-E) or mice infected with Theiler's murine encephalomyelitis virus (TMEV) for 12 h (F-J), 24 h (K-O), or 48 h (P-T) were killed by intracardiac perfusion of 4% paraformaldehyde and vibratome sections of brain were prepared and stained with CD45 (A, B, F, G, K, L, P, Q), CD11b (C, H, M, R), Gr1 (D, I, N, S), or 1A8 (E, J, O, T). No staining for any of the markers was observed in the uninfected brain (A-E). The number of CD45-labeled cells increased within the hippocampal region through 12, 24, and 48 hpi (F, K, P). Higher magnification of a cross section showing the corpus callosum and alveus (top of each image), the CA1 pyramidal neuron layer (middle of each image), and the hippocampal fissure (bottom of each image) (B-E, G-J, L-O, Q-T) confirms the increasing density of the CD45+ infiltrate and also reveals that the Gr1+ population peaks at 24 h (N) while the 1A8+ population continues to increase through time (J, O, T). The scale bar in P is 1 mm and refers to (A), (F), and (K). The scale bar in T is 200 μm and refers to the remaining panels. Results are representative of more than five mice at each timepoint.
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Figure 8: Visualization of the timecourse of neutrophil and inflammatory monocyte infiltration during acute infection. Uninfected mice (A-E) or mice infected with Theiler's murine encephalomyelitis virus (TMEV) for 12 h (F-J), 24 h (K-O), or 48 h (P-T) were killed by intracardiac perfusion of 4% paraformaldehyde and vibratome sections of brain were prepared and stained with CD45 (A, B, F, G, K, L, P, Q), CD11b (C, H, M, R), Gr1 (D, I, N, S), or 1A8 (E, J, O, T). No staining for any of the markers was observed in the uninfected brain (A-E). The number of CD45-labeled cells increased within the hippocampal region through 12, 24, and 48 hpi (F, K, P). Higher magnification of a cross section showing the corpus callosum and alveus (top of each image), the CA1 pyramidal neuron layer (middle of each image), and the hippocampal fissure (bottom of each image) (B-E, G-J, L-O, Q-T) confirms the increasing density of the CD45+ infiltrate and also reveals that the Gr1+ population peaks at 24 h (N) while the 1A8+ population continues to increase through time (J, O, T). The scale bar in P is 1 mm and refers to (A), (F), and (K). The scale bar in T is 200 μm and refers to the remaining panels. Results are representative of more than five mice at each timepoint.

Mentions: Immunostaining brain sections at these time points revealed a growing population of CD45+ cells in the hippocampal fissure and in the superior white matter tracts (Figure 8A, B, F, G, K, L, P, Q). Many of these cells were CD11b+ (Figure 8C, H, M, R) and a strong population of Gr1+ cells was observed at 24 hpi (Figure 8N) but was greatly decreased by 48 hpi (Figure 8S). Likewise, 1A8+ cells were clearly present in the hippocampus at 12, 24, and 48 hpi (Figure 8J, O, T). The relative differences in number of cells labeled with each of these markers is hard to interpret, especially given the overall difficulty in successfully immunostaining for several of the markers. Nonetheless, Figure 8 indicates that the hippocampus is a target for the rapid infiltration of CD45+CD11b+Gr1+ and CD45+CD11b+1A8+ cells, confirming the findings at 18 hpi in the LysM:GFP mice (Figure 5, Figure 6) and providing anatomic localization to the observations in Figure 7.


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

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

Visualization of the timecourse of neutrophil and inflammatory monocyte infiltration during acute infection. Uninfected mice (A-E) or mice infected with Theiler's murine encephalomyelitis virus (TMEV) for 12 h (F-J), 24 h (K-O), or 48 h (P-T) were killed by intracardiac perfusion of 4% paraformaldehyde and vibratome sections of brain were prepared and stained with CD45 (A, B, F, G, K, L, P, Q), CD11b (C, H, M, R), Gr1 (D, I, N, S), or 1A8 (E, J, O, T). No staining for any of the markers was observed in the uninfected brain (A-E). The number of CD45-labeled cells increased within the hippocampal region through 12, 24, and 48 hpi (F, K, P). Higher magnification of a cross section showing the corpus callosum and alveus (top of each image), the CA1 pyramidal neuron layer (middle of each image), and the hippocampal fissure (bottom of each image) (B-E, G-J, L-O, Q-T) confirms the increasing density of the CD45+ infiltrate and also reveals that the Gr1+ population peaks at 24 h (N) while the 1A8+ population continues to increase through time (J, O, T). The scale bar in P is 1 mm and refers to (A), (F), and (K). The scale bar in T is 200 μm and refers to the remaining panels. Results are representative of more than five mice at each timepoint.
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Figure 8: Visualization of the timecourse of neutrophil and inflammatory monocyte infiltration during acute infection. Uninfected mice (A-E) or mice infected with Theiler's murine encephalomyelitis virus (TMEV) for 12 h (F-J), 24 h (K-O), or 48 h (P-T) were killed by intracardiac perfusion of 4% paraformaldehyde and vibratome sections of brain were prepared and stained with CD45 (A, B, F, G, K, L, P, Q), CD11b (C, H, M, R), Gr1 (D, I, N, S), or 1A8 (E, J, O, T). No staining for any of the markers was observed in the uninfected brain (A-E). The number of CD45-labeled cells increased within the hippocampal region through 12, 24, and 48 hpi (F, K, P). Higher magnification of a cross section showing the corpus callosum and alveus (top of each image), the CA1 pyramidal neuron layer (middle of each image), and the hippocampal fissure (bottom of each image) (B-E, G-J, L-O, Q-T) confirms the increasing density of the CD45+ infiltrate and also reveals that the Gr1+ population peaks at 24 h (N) while the 1A8+ population continues to increase through time (J, O, T). The scale bar in P is 1 mm and refers to (A), (F), and (K). The scale bar in T is 200 μm and refers to the remaining panels. Results are representative of more than five mice at each timepoint.
Mentions: Immunostaining brain sections at these time points revealed a growing population of CD45+ cells in the hippocampal fissure and in the superior white matter tracts (Figure 8A, B, F, G, K, L, P, Q). Many of these cells were CD11b+ (Figure 8C, H, M, R) and a strong population of Gr1+ cells was observed at 24 hpi (Figure 8N) but was greatly decreased by 48 hpi (Figure 8S). Likewise, 1A8+ cells were clearly present in the hippocampus at 12, 24, and 48 hpi (Figure 8J, O, T). The relative differences in number of cells labeled with each of these markers is hard to interpret, especially given the overall difficulty in successfully immunostaining for several of the markers. Nonetheless, Figure 8 indicates that the hippocampus is a target for the rapid infiltration of CD45+CD11b+Gr1+ and CD45+CD11b+1A8+ cells, confirming the findings at 18 hpi in the LysM:GFP mice (Figure 5, Figure 6) and providing anatomic localization to the observations in Figure 7.

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