Neisseria meningitidiselicits a pro-inflammatory response involving IκBζ in a human blood-cerebrospinal fluid barrier model

Julia Borkowski,Hiroshi Ishikawa,Li Li,Horst Schroten,Tobias Tenenbaum,Peter Findeisen,Norbert Gretz,Christel Weiss,Carolin Stump-Guthier,Ulrike Steinmann,Natascha Quednau,Christian Schwerk

doi:10.1186/s12974-014-0163-x

Abstract

BackgroundThe human-specific, Gram-negative bacterium Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis worldwide. The blood-cerebrospinal fluid barrier (BCSFB), which is constituted by the epithelial cells of the choroid plexus (CP), has been suggested as one of the potential entry sites of Nm into the CSF and can contribute to the inflammatory response during infectious diseases of the brain. Toll-like receptors (TLRs) are involved in mediating signal transduction caused by the pathogens.MethodsUsing a recently established in vitro model of the human BCSFB based on human malignant CP papilloma (HIBCPP) cells we investigated the cellular response of HIBCPP cells challenged with the meningitis-causing Nm strain, MC58, employing transcriptome and RT-PCR analysis, cytokine bead array, and enzyme-linked immunosorbent assay (ELISA). In comparison, we analyzed the answer to the closely related unencapsulated carrier isolate Nm α14. The presence of TLRs in HIBCPP and their role during signal transduction caused by Nm was studied by RT-PCR and the use of specific agonists and mutant bacteria.ResultsWe observed a stronger transcriptional response after infection with strain MC58, in particular with its capsule-deficient mutant MC58siaD−, which correlated with bacterial invasion levels. Expression evaluation and Gene Set Enrichment Analysis pointed to a NFκB-mediated pro-inflammatory immune response involving up-regulation of the transcription factor IκBζ. Infected cells secreted significant levels of pro-inflammatory chemokines and cytokines, including, among others, IL8, CXCL1-3, and the IκBζ target gene product IL6. The expression profile of pattern recognition receptors in HIBCPP cells and the response to specific agonists indicates that TLR2/TLR6, rather than TLR4 or TLR2/TLR1, is involved in the cellular reaction following Nm infection.ConclusionsOur data show that Nm can initiate a pro-inflammatory response in human CP epithelial cells probably involving TLR2/TLR6 signaling and the transcriptional regulator IκBζ.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-014-0163-x) contains supplementary material, which is available to authorized users.

Highlights

The human-specific, Gram-negative bacterium Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis worldwide
There is evidence that during an infection Nm interacts with the basolateral side of CP epithelial cells [5,6] and in an in vitro model of the blood-cerebrospinal fluid barrier (BCSFB) based on human choroid plexus papilloma (HIBCPP) cells Neisseria can enter and transmigrate across these CP epithelial cells by invasion from the physiologically relevant basolateral blood side [7]
A neisserial carrier isolate invades Human choroid plexus papilloma (HIBCPP) cells only marginally from the basolateral side We have previously shown that the Nm strain MC58, a disease isolate, invades HIBCPP cells polar from the physiologically-relevant basolateral side with the capsule attenuating invasion properties [7]

Summary

Introduction

The human-specific, Gram-negative bacterium Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis worldwide. The blood-cerebrospinal fluid barrier (BCSFB), which is constituted by the epithelial cells of the choroid plexus (CP), has been suggested as one of the potential entry sites of Nm into the CSF and can contribute to the inflammatory response during infectious diseases of the brain. There is evidence that during an infection Nm interacts with the basolateral side of CP epithelial cells [5,6] and in an in vitro model of the BCSFB based on human choroid plexus papilloma (HIBCPP) cells Neisseria can enter and transmigrate across these CP epithelial cells by invasion from the physiologically relevant basolateral blood side [7]. An important virulence factor of Nm during the progress of meningitis is the bacterial capsule [8], and capsule-deficient mutants displayed higher invasion rates into HIBCPP cells in vitro [7]

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