Adjuvant TACE inhibitor treatment improves the outcome of TLR2-/-mice with experimental pneumococcal meningitis

Hakim Echchannaoui,Stephen L Leib,Regine Ma Landmann,Ulf Neumann

doi:10.1186/1471-2334-7-25

Abstract

BackgroundStreptococcus (S.) pneumoniae meningitis has a high lethality despite antibiotic treatment. Inflammation is a major pathogenetic factor, which is unresponsive to antibiotics. Therefore adjunctive therapies with antiinflammatory compounds have been developed. TNF484 is a TNF-alpha converting enzyme (TACE) inhibitor and has been found efficacious in experimental meningitis. Toll-like receptor 2 (TLR2) contributes to host response in pneumococcal meningitis by enhancing bacterial clearing and downmodulating inflammation. In this study, TNF484 was applied in mice, which lacked TLR2 and exhibited a strong meningeal inflammation.Methods103 CFU S. pneumoniae serotype 3 was inoculated subarachnoidally into C57BL/6 wild type (wt) mice or TLR2-/-, CD14-/- and CD14-/-/TLR2-/- mice. Severity of disease and survival was followed over 9 days. Response to antibiotics (80 mg/kg ceftriaxone i.p. for 5 days) and/or TACE inhibitor treatment (1 mg/kg s.c. twice daily for 4 days) was evaluated. Animals were sacrificed after 12, 24, and 48 h for analysis of bacterial load in cerebrospinal fluid (CSF) and brain and for TNF and leukocyte measurements in CSF.ResultsTLR2-/- mice were significantly sicker than the other mouse strains 24 h after infection. All knockout mice showed higher disease severity after 48 h and died earlier than wt mice. TNF release into CSF was significantly more elevated in TLR2-/- than in the other strains after 24 h. Brain bacterial numbers were significantly higher in all knockout than wt mice after 24 h. Modulation of outcome by antibiotic and TACE inhibitor treatment was evaluated. With antibiotic therapy all wt, CD14-/- and TLR2-/-/CD14-/- mice, but only 79% of TLR2-/- mice, were rescued. TACE inhibitor treatment alone did not rescue, but prolonged survival in wt mice, and in TLR2-/- and CD14-/- mice to the values observed in untreated wt mice. By combined antibiotic and TACE inhibitor treatment 95% of TLR2-/- mice were rescued.ConclusionDuring pneumococcal meningitis strong inflammation in TLR2-deficiency was associated with incomplete responsiveness to antibiotics and complete response to combined antibiotic and TACE inhibitor treatment. TACE inhibitor treatment offers a promising adjuvant therapeutic strategy in pneumococcal meningitis.

Highlights

Streptococcus (S.) pneumoniae meningitis has a high lethality despite antibiotic treatment
We found a shorter survival in CD14-/- than in wt mice, which was due to enhanced CXCR2 expression leading to early recruitment of leukocyte and increased TNF in cerebrospinal fluid (CSF) [18]
Bacterial numbers in CSF were similar in all strains 24 h after infection, indicating that planctonic bacteria recovered in CSF did not represent an early pathogenetic factor, which contributed to the more severe clinical picture of the Toll-like receptor 2 (TLR2)-/- strain

Summary

Introduction

Streptococcus (S.) pneumoniae meningitis has a high lethality despite antibiotic treatment. Besides TLR2, CD14 was recognized as receptor for Gram-positive cell wall components [16,17] It is poorly expressed in resting mouse phagocytes [18] and strongly induced upon stimulation with bacterial components or infection in vitro and in vivo [18,19]. From our in vivo studies using single knockout mice, it appears that TLR2 and CD14 both are protective in meningitis, by different mechanisms Because both strains showed excessive TNF, we compared the treatment response in wt, TLR2-/-, CD14-/-, and CD14-/-/TLR2-/-double knockout mice with meningitis to antibiotic treatment and/or anti-inflammatory treatment with TACE inhibitor

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Results

Discussion

Conclusion