Front Microbiol. 2015 Dec 1;6:1340. doi: 10.3389/fmicb.2015.01340. eCollection 2015.

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

Pettini E1, Fiorino F1, Cuppone AM1, Iannelli F1, Medaglini D1, Pozzi G1.

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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.

KEYWORDS:

IFN-γ; Streptococcus pneumoniae; TIGR4; intracranial infection; meningitis; murine model

PMID: 26648922 [PubMed] PMCID: PMC4664635