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TLR7-mediated skin inflammation remotely triggers chemokine expression and leukocyte accumulation in the brain.

McColl A, Thomson CA, Nerurkar L, Graham GJ, Cavanagh J - J Neuroinflammation (2016)

Bottom Line: Here we use a well-characterised animal model of psoriasis-like skin inflammation-imiquimod-to investigate the effects of tissue-specific peripheral inflammation on the brain.We found that a number of genes are upregulated in the brain following treatment, amongst which is a subset of inflammatory chemokines (CCL3, CCL5, CCL9, CXCL10, CXCL13, CXCL16 and CCR5).Strikingly, this model induced the infiltration of a number of immune cell subsets into the brain parenchyma, including T cells, NK cells and myeloid cells, along with a reduction in neurogenesis and a suppression of burrowing activity.

View Article: PubMed Central - PubMed

Affiliation: Institute of Infection, Immunity & Inflammation, College of Medical & Veterinary Life Sciences, University of Glasgow, 120 University Place, Glasgow, G12 8TA, UK.

ABSTRACT

Background: The relationship between the brain and the immune system has become increasingly topical as, although it is immune-specialised, the CNS is not free from the influences of the immune system. Recent data indicate that peripheral immune stimulation can significantly affect the CNS. But the mechanisms underpinning this relationship remain unclear. The standard approach to understanding this relationship has relied on systemic immune activation using bacterial components, finding that immune mediators, such as cytokines, can have a significant effect on brain function and behaviour. More rarely have studies used disease models that are representative of human disorders.

Methods: Here we use a well-characterised animal model of psoriasis-like skin inflammation-imiquimod-to investigate the effects of tissue-specific peripheral inflammation on the brain. We used full genome array, flow cytometry analysis of immune cell infiltration, doublecortin staining for neural precursor cells and a behavioural read-out exploiting natural burrowing behaviour.

Results: We found that a number of genes are upregulated in the brain following treatment, amongst which is a subset of inflammatory chemokines (CCL3, CCL5, CCL9, CXCL10, CXCL13, CXCL16 and CCR5). Strikingly, this model induced the infiltration of a number of immune cell subsets into the brain parenchyma, including T cells, NK cells and myeloid cells, along with a reduction in neurogenesis and a suppression of burrowing activity.

Conclusions: These findings demonstrate that cutaneous, peripheral immune stimulation is associated with significant leukocyte infiltration into the brain and suggest that chemokines may be amongst the key mediators driving this response.

No MeSH data available.


Related in: MedlinePlus

Aldara treatment induces the infiltration of monocytes, but not neutrophils, into the brain. Mice were treated with 80-mg Aldara cream or control cream every 24 h for one, three or five consecutive days. Mice were euthanised 24 h following the final application. a Protein expression of CCL2 in whole brain lysate was assessed in control and treated brains 4 h, 12 h, 1 day, 3 days and 5 days after treatment. b Perfused brains were homogenised, and a single cell suspension was generated as described. Cells were labelled with fluorescent antibodies. CD45hiCD11b+ cells were selected following dead cell exclusion and doublet exclusion, and representative gating strategy based on expression of Ly6C, Ly6G and CD64 is shown. c Counts per million cells were generated using total cell counts and are shown for neutrophils, monocytes, differentiating monocytes (population 2) and macrophages (population 3) at 1, 3 and 5 days following Aldara treatment. n = 4 mice per group. Significance was determined using one- (a) or two-way (b, c) ANOVA with Bonferroni multiple comparison post-tests. Data presented in a were log transformed prior to statistical analysis ****p < 0.0001 ***p ≤ 0.001 **p ≤ 0.01 *p ≤ 0.05
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Fig4: Aldara treatment induces the infiltration of monocytes, but not neutrophils, into the brain. Mice were treated with 80-mg Aldara cream or control cream every 24 h for one, three or five consecutive days. Mice were euthanised 24 h following the final application. a Protein expression of CCL2 in whole brain lysate was assessed in control and treated brains 4 h, 12 h, 1 day, 3 days and 5 days after treatment. b Perfused brains were homogenised, and a single cell suspension was generated as described. Cells were labelled with fluorescent antibodies. CD45hiCD11b+ cells were selected following dead cell exclusion and doublet exclusion, and representative gating strategy based on expression of Ly6C, Ly6G and CD64 is shown. c Counts per million cells were generated using total cell counts and are shown for neutrophils, monocytes, differentiating monocytes (population 2) and macrophages (population 3) at 1, 3 and 5 days following Aldara treatment. n = 4 mice per group. Significance was determined using one- (a) or two-way (b, c) ANOVA with Bonferroni multiple comparison post-tests. Data presented in a were log transformed prior to statistical analysis ****p < 0.0001 ***p ≤ 0.001 **p ≤ 0.01 *p ≤ 0.05

Mentions: Monocytes are early responders to infection and have been shown to infiltrate the brain in peripheral inflammatory models and in response to viral infections that invade the central nervous system [44]. Interestingly, several of the chemokine transcripts that are elevated in the brain in response to topical Aldara treatment, specifically Ccl3, Ccl5 and Ccl9, are known to recruit monocytes to sites of inflammation. In addition, protein analysis from an independent experiment clearly demonstrates that levels of CCL2, a classic monocyte chemoattractant, are also elevated in the brain following Aldara treatment (Fig. 4a). As shown in Additional file 6: Figure S4B, the treated brain appears to be devoid of infiltrating leukocytes at day 1. This prompted us to also analyse chemokine levels at two earlier time points, 4 and 12 h after treatment in order to capture the protein signal before and after leukocyte infiltration. Interestingly, CCL2 was significantly elevated in the brain from as early as 4 h following topical Aldara treatment and prior to leukocyte infiltration (Fig. 4a) These data suggest that CCL2 is likely to be produced by brain-resident cells, rather than the infiltrating leukocytes themselves.Fig. 4


TLR7-mediated skin inflammation remotely triggers chemokine expression and leukocyte accumulation in the brain.

McColl A, Thomson CA, Nerurkar L, Graham GJ, Cavanagh J - J Neuroinflammation (2016)

Aldara treatment induces the infiltration of monocytes, but not neutrophils, into the brain. Mice were treated with 80-mg Aldara cream or control cream every 24 h for one, three or five consecutive days. Mice were euthanised 24 h following the final application. a Protein expression of CCL2 in whole brain lysate was assessed in control and treated brains 4 h, 12 h, 1 day, 3 days and 5 days after treatment. b Perfused brains were homogenised, and a single cell suspension was generated as described. Cells were labelled with fluorescent antibodies. CD45hiCD11b+ cells were selected following dead cell exclusion and doublet exclusion, and representative gating strategy based on expression of Ly6C, Ly6G and CD64 is shown. c Counts per million cells were generated using total cell counts and are shown for neutrophils, monocytes, differentiating monocytes (population 2) and macrophages (population 3) at 1, 3 and 5 days following Aldara treatment. n = 4 mice per group. Significance was determined using one- (a) or two-way (b, c) ANOVA with Bonferroni multiple comparison post-tests. Data presented in a were log transformed prior to statistical analysis ****p < 0.0001 ***p ≤ 0.001 **p ≤ 0.01 *p ≤ 0.05
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Fig4: Aldara treatment induces the infiltration of monocytes, but not neutrophils, into the brain. Mice were treated with 80-mg Aldara cream or control cream every 24 h for one, three or five consecutive days. Mice were euthanised 24 h following the final application. a Protein expression of CCL2 in whole brain lysate was assessed in control and treated brains 4 h, 12 h, 1 day, 3 days and 5 days after treatment. b Perfused brains were homogenised, and a single cell suspension was generated as described. Cells were labelled with fluorescent antibodies. CD45hiCD11b+ cells were selected following dead cell exclusion and doublet exclusion, and representative gating strategy based on expression of Ly6C, Ly6G and CD64 is shown. c Counts per million cells were generated using total cell counts and are shown for neutrophils, monocytes, differentiating monocytes (population 2) and macrophages (population 3) at 1, 3 and 5 days following Aldara treatment. n = 4 mice per group. Significance was determined using one- (a) or two-way (b, c) ANOVA with Bonferroni multiple comparison post-tests. Data presented in a were log transformed prior to statistical analysis ****p < 0.0001 ***p ≤ 0.001 **p ≤ 0.01 *p ≤ 0.05
Mentions: Monocytes are early responders to infection and have been shown to infiltrate the brain in peripheral inflammatory models and in response to viral infections that invade the central nervous system [44]. Interestingly, several of the chemokine transcripts that are elevated in the brain in response to topical Aldara treatment, specifically Ccl3, Ccl5 and Ccl9, are known to recruit monocytes to sites of inflammation. In addition, protein analysis from an independent experiment clearly demonstrates that levels of CCL2, a classic monocyte chemoattractant, are also elevated in the brain following Aldara treatment (Fig. 4a). As shown in Additional file 6: Figure S4B, the treated brain appears to be devoid of infiltrating leukocytes at day 1. This prompted us to also analyse chemokine levels at two earlier time points, 4 and 12 h after treatment in order to capture the protein signal before and after leukocyte infiltration. Interestingly, CCL2 was significantly elevated in the brain from as early as 4 h following topical Aldara treatment and prior to leukocyte infiltration (Fig. 4a) These data suggest that CCL2 is likely to be produced by brain-resident cells, rather than the infiltrating leukocytes themselves.Fig. 4

Bottom Line: Here we use a well-characterised animal model of psoriasis-like skin inflammation-imiquimod-to investigate the effects of tissue-specific peripheral inflammation on the brain.We found that a number of genes are upregulated in the brain following treatment, amongst which is a subset of inflammatory chemokines (CCL3, CCL5, CCL9, CXCL10, CXCL13, CXCL16 and CCR5).Strikingly, this model induced the infiltration of a number of immune cell subsets into the brain parenchyma, including T cells, NK cells and myeloid cells, along with a reduction in neurogenesis and a suppression of burrowing activity.

View Article: PubMed Central - PubMed

Affiliation: Institute of Infection, Immunity & Inflammation, College of Medical & Veterinary Life Sciences, University of Glasgow, 120 University Place, Glasgow, G12 8TA, UK.

ABSTRACT

Background: The relationship between the brain and the immune system has become increasingly topical as, although it is immune-specialised, the CNS is not free from the influences of the immune system. Recent data indicate that peripheral immune stimulation can significantly affect the CNS. But the mechanisms underpinning this relationship remain unclear. The standard approach to understanding this relationship has relied on systemic immune activation using bacterial components, finding that immune mediators, such as cytokines, can have a significant effect on brain function and behaviour. More rarely have studies used disease models that are representative of human disorders.

Methods: Here we use a well-characterised animal model of psoriasis-like skin inflammation-imiquimod-to investigate the effects of tissue-specific peripheral inflammation on the brain. We used full genome array, flow cytometry analysis of immune cell infiltration, doublecortin staining for neural precursor cells and a behavioural read-out exploiting natural burrowing behaviour.

Results: We found that a number of genes are upregulated in the brain following treatment, amongst which is a subset of inflammatory chemokines (CCL3, CCL5, CCL9, CXCL10, CXCL13, CXCL16 and CCR5). Strikingly, this model induced the infiltration of a number of immune cell subsets into the brain parenchyma, including T cells, NK cells and myeloid cells, along with a reduction in neurogenesis and a suppression of burrowing activity.

Conclusions: These findings demonstrate that cutaneous, peripheral immune stimulation is associated with significant leukocyte infiltration into the brain and suggest that chemokines may be amongst the key mediators driving this response.

No MeSH data available.


Related in: MedlinePlus