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Interferon-γ from Brain Leukocytes Enhances Meningitis by Type 4 Streptococcus pneumoniae.

Pettini E, Fiorino F, Cuppone AM, Iannelli F, Medaglini D, Pozzi G - Front Microbiol (2015)

Bottom Line: The amount of lymphocytes, NK cells, neutrophils, monocytes and macrophages in the brain increased 48 h post infection.Pro-inflammatory cytokines such as IL-1β and TNF-α, and TLR2 were also upregulated.This study shows that IFN-γ produced during meningitis by type 4 S. pneumoniae enhances bacterial pathogenesis exerting a negative effect on the disease outcome.

View Article: PubMed Central - PubMed

Affiliation: Laboratorio di Microbiologia Molecolare e Biotecnologia, Dipartimento di Biotecnologie Mediche, Università degli Studi di Siena Siena, Italy.

ABSTRACT
Streptococcus pneumoniae is the leading cause of bacterial meningitis. Pneumococcal meningitis is a life-threatening disease with high rates of mortality and neurological sequelae. Immune targeting of S. pneumoniae is essential for clearance of infection; however, within the brain, the induced inflammatory response contributes to pathogenesis. In this study we investigate the local inflammatory response and the role of IFN-γ in a murine model of pneumococcal meningitis induced by intracranial injection of type 4 S. pneumoniae. Lymphoid and myeloid cell populations involved in meningitis, as well as cytokine gene expression, were investigated after infection. Animals were treated with a monoclonal antibody specific for murine IFN-γ to evaluate its role in animal survival. Intracranial inoculation of 3 × 10(4) colony-forming units of type 4 strain TIGR4 caused 75% of mice to develop meningitis within 4 days. The amount of lymphocytes, NK cells, neutrophils, monocytes and macrophages in the brain increased 48 h post infection. IFN-γ mRNA levels were about 240-fold higher in brains of infected mice compared to controls. Pro-inflammatory cytokines such as IL-1β and TNF-α, and TLR2 were also upregulated. In vivo treatment with anti-IFN-γ antibody increased survival of infected mice. This study shows that IFN-γ produced during meningitis by type 4 S. pneumoniae enhances bacterial pathogenesis exerting a negative effect on the disease outcome.

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Related in: MedlinePlus

Cellular source of IFN-γ in the infected brain. Lymphocytes (CD45hiCD3+), NKs (CD45hiCD3−NKp46+), neutrophils (CD45hiCD11bhiLy6G+), monocytes (CD45hiCD11bhi Ly6G−Ly6C+), and macrophages (CD45hiCD11bhiF4/80+) were analyzed for IFN-γ intracellular staining. Flow cytometric analysis was performed in brain of mice 48 h post intracranial infection with 3 × 104 CFU of S. pneumoniae TIGR4. (A) Representative flow cytometry dot plot graphs showing the percentage of IFN-γ+ cells among different cell populations in the brain. The gate for IFN-γ+ cells was set using an appropriate APC-conjugated isotype control. (B) Symbols represent individual mice and bars represent the mean. Mean values for each cell population were 0.6 ± 0.1% for lymphocytes, 7 ± 2.4% for NK cells, 1.8 ± 0.4% for neutrophils, 3.4 ± 0.8% for monocytes, and 3 ± 0.9% for macrophages.
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Figure 4: Cellular source of IFN-γ in the infected brain. Lymphocytes (CD45hiCD3+), NKs (CD45hiCD3−NKp46+), neutrophils (CD45hiCD11bhiLy6G+), monocytes (CD45hiCD11bhi Ly6G−Ly6C+), and macrophages (CD45hiCD11bhiF4/80+) were analyzed for IFN-γ intracellular staining. Flow cytometric analysis was performed in brain of mice 48 h post intracranial infection with 3 × 104 CFU of S. pneumoniae TIGR4. (A) Representative flow cytometry dot plot graphs showing the percentage of IFN-γ+ cells among different cell populations in the brain. The gate for IFN-γ+ cells was set using an appropriate APC-conjugated isotype control. (B) Symbols represent individual mice and bars represent the mean. Mean values for each cell population were 0.6 ± 0.1% for lymphocytes, 7 ± 2.4% for NK cells, 1.8 ± 0.4% for neutrophils, 3.4 ± 0.8% for monocytes, and 3 ± 0.9% for macrophages.

Mentions: To characterize pneumococcal meningitis, leukocyte recruitment was analyzed in brains of mice with meningitis 48 h post infection with TIGR4 (n = 3–6 mice/group in four independent experiments) (Figures 3A,B) and the source of IFN-γ was investigated by flow cytometric analysis (Figure 4). The average number of leukocytes (CD45+ live cells) detected in mice was about 6.4 × 104/brain. Neutrophils (CD45hiCD11bhiLy6G+ cells) were the most abundant cell population in the inflammatory infiltrate detected in TIGR4 infected brains, representing the 27.4 ± 6.5% (mean ± SEM) of CD45+ cells (P < 0.001 vs. control, Figure 3B). Within the leukocyte population detected in the brain of TIGR4 infected mice, was also observed a significant increase of monocytes (CD45hiCD11bhiLy6G−Ly6C+ cells) representing the 20.7 ± 3.1% of CD45+ cells (P < 0.001), macrophages (CD45hiCD11bhiF4/80+ cells) with the 18.6 ± 4% (P < 0.001), lymphocytes (CD45hiCD3+ cells) with the 3.9 ± 0.5% (P < 0.001) and NKs (CD45hiCD3−NKp46+ cells) with the 5 ± 1% (P < 0.001) (Figure 3B). B cells (CD45hiB220+ cells) were also investigated and corresponded to 0.3 ± 0.1% of leukocytes (data not shown). In the brain of control mice, injected with bacterial growth medium, only few leukocytes were observed with 0.4 ± 0.3% of neutrophils, 0.07 ± 0.04% of monocytes, 0.3 ± 0.1% of macrophages, 0.4 ± 0.15% of lymphocytes and 0.7 ± 0.15% of NK cells.


Interferon-γ from Brain Leukocytes Enhances Meningitis by Type 4 Streptococcus pneumoniae.

Pettini E, Fiorino F, Cuppone AM, Iannelli F, Medaglini D, Pozzi G - Front Microbiol (2015)

Cellular source of IFN-γ in the infected brain. Lymphocytes (CD45hiCD3+), NKs (CD45hiCD3−NKp46+), neutrophils (CD45hiCD11bhiLy6G+), monocytes (CD45hiCD11bhi Ly6G−Ly6C+), and macrophages (CD45hiCD11bhiF4/80+) were analyzed for IFN-γ intracellular staining. Flow cytometric analysis was performed in brain of mice 48 h post intracranial infection with 3 × 104 CFU of S. pneumoniae TIGR4. (A) Representative flow cytometry dot plot graphs showing the percentage of IFN-γ+ cells among different cell populations in the brain. The gate for IFN-γ+ cells was set using an appropriate APC-conjugated isotype control. (B) Symbols represent individual mice and bars represent the mean. Mean values for each cell population were 0.6 ± 0.1% for lymphocytes, 7 ± 2.4% for NK cells, 1.8 ± 0.4% for neutrophils, 3.4 ± 0.8% for monocytes, and 3 ± 0.9% for macrophages.
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Figure 4: Cellular source of IFN-γ in the infected brain. Lymphocytes (CD45hiCD3+), NKs (CD45hiCD3−NKp46+), neutrophils (CD45hiCD11bhiLy6G+), monocytes (CD45hiCD11bhi Ly6G−Ly6C+), and macrophages (CD45hiCD11bhiF4/80+) were analyzed for IFN-γ intracellular staining. Flow cytometric analysis was performed in brain of mice 48 h post intracranial infection with 3 × 104 CFU of S. pneumoniae TIGR4. (A) Representative flow cytometry dot plot graphs showing the percentage of IFN-γ+ cells among different cell populations in the brain. The gate for IFN-γ+ cells was set using an appropriate APC-conjugated isotype control. (B) Symbols represent individual mice and bars represent the mean. Mean values for each cell population were 0.6 ± 0.1% for lymphocytes, 7 ± 2.4% for NK cells, 1.8 ± 0.4% for neutrophils, 3.4 ± 0.8% for monocytes, and 3 ± 0.9% for macrophages.
Mentions: To characterize pneumococcal meningitis, leukocyte recruitment was analyzed in brains of mice with meningitis 48 h post infection with TIGR4 (n = 3–6 mice/group in four independent experiments) (Figures 3A,B) and the source of IFN-γ was investigated by flow cytometric analysis (Figure 4). The average number of leukocytes (CD45+ live cells) detected in mice was about 6.4 × 104/brain. Neutrophils (CD45hiCD11bhiLy6G+ cells) were the most abundant cell population in the inflammatory infiltrate detected in TIGR4 infected brains, representing the 27.4 ± 6.5% (mean ± SEM) of CD45+ cells (P < 0.001 vs. control, Figure 3B). Within the leukocyte population detected in the brain of TIGR4 infected mice, was also observed a significant increase of monocytes (CD45hiCD11bhiLy6G−Ly6C+ cells) representing the 20.7 ± 3.1% of CD45+ cells (P < 0.001), macrophages (CD45hiCD11bhiF4/80+ cells) with the 18.6 ± 4% (P < 0.001), lymphocytes (CD45hiCD3+ cells) with the 3.9 ± 0.5% (P < 0.001) and NKs (CD45hiCD3−NKp46+ cells) with the 5 ± 1% (P < 0.001) (Figure 3B). B cells (CD45hiB220+ cells) were also investigated and corresponded to 0.3 ± 0.1% of leukocytes (data not shown). In the brain of control mice, injected with bacterial growth medium, only few leukocytes were observed with 0.4 ± 0.3% of neutrophils, 0.07 ± 0.04% of monocytes, 0.3 ± 0.1% of macrophages, 0.4 ± 0.15% of lymphocytes and 0.7 ± 0.15% of NK cells.

Bottom Line: The amount of lymphocytes, NK cells, neutrophils, monocytes and macrophages in the brain increased 48 h post infection.Pro-inflammatory cytokines such as IL-1β and TNF-α, and TLR2 were also upregulated.This study shows that IFN-γ produced during meningitis by type 4 S. pneumoniae enhances bacterial pathogenesis exerting a negative effect on the disease outcome.

View Article: PubMed Central - PubMed

Affiliation: Laboratorio di Microbiologia Molecolare e Biotecnologia, Dipartimento di Biotecnologie Mediche, Università degli Studi di Siena Siena, Italy.

ABSTRACT
Streptococcus pneumoniae is the leading cause of bacterial meningitis. Pneumococcal meningitis is a life-threatening disease with high rates of mortality and neurological sequelae. Immune targeting of S. pneumoniae is essential for clearance of infection; however, within the brain, the induced inflammatory response contributes to pathogenesis. In this study we investigate the local inflammatory response and the role of IFN-γ in a murine model of pneumococcal meningitis induced by intracranial injection of type 4 S. pneumoniae. Lymphoid and myeloid cell populations involved in meningitis, as well as cytokine gene expression, were investigated after infection. Animals were treated with a monoclonal antibody specific for murine IFN-γ to evaluate its role in animal survival. Intracranial inoculation of 3 × 10(4) colony-forming units of type 4 strain TIGR4 caused 75% of mice to develop meningitis within 4 days. The amount of lymphocytes, NK cells, neutrophils, monocytes and macrophages in the brain increased 48 h post infection. IFN-γ mRNA levels were about 240-fold higher in brains of infected mice compared to controls. Pro-inflammatory cytokines such as IL-1β and TNF-α, and TLR2 were also upregulated. In vivo treatment with anti-IFN-γ antibody increased survival of infected mice. This study shows that IFN-γ produced during meningitis by type 4 S. pneumoniae enhances bacterial pathogenesis exerting a negative effect on the disease outcome.

No MeSH data available.


Related in: MedlinePlus