A Model System to Investigate Translocation of Neisseria meningitidis

Thomas C. Sutherland & Prof. C. Tang Centre for Molecular Microbiology and Infection, Flowers Building, Imperial College London

Figure 1 – N. meningitidis infection of Calu-3 cells

• Calu-3 cells have not previously been infected with N. meningitidis. Test infections demonstrate that they undergo a similar pattern of infection to the more studied ‘Chang’ cell line (A).

• Type IV Pilus dependant adhesion, previously documented in other cell lines2 is also observed in the Calu-3 cells (B & C).

A B

C

Figure 2 – Optimising the cell culture conditionsA B

• Trans-epithelial electrical resistance (TEER) develops as tight junctions form and is a good indicator of monolayer polarisation. Unpolarised cells generate TEER readings of 0-100Ω.

• Coating cell culture inserts with extracellular matrix proteins affects the development of TEER. A 1:1 mixture of laminin and fibronectin is most effective (A). Optimisation culture procedure allows reliable generation of TEER (B).

Figure 3 – Morphology of the cultured cell layers

• TEM (cross sections, 120 hrs post seeding) and Confocal microscopy (monolayers viewed from above, 120 hrs post seeding) demonstrate that the cultured cells reliably form confluent, polarised monolayers with all the morphological features of a polarised epithelium.

Monolayer of Calu-3 cells on the cell culture membrane (CCM). Apical (AP)/basal (BA) differentiation, the formation of tight junctions (TJ), desmosomes (D) and microvilli (MV) are clearly all visible.

CCM

BA

AP

MVTJ

TJ

D

TJ

D

AB

The Junctional complex (JC) consisting of tight junctions, the adhesion belt and desmosomes.

JC

A B

TJ

ZO-1 Occludin

Detail of Tight Junctions: TEM shows tight association of cell membranes, while IF staining shows presence of tight junction proteins Occludin and ZO-1.

C

Desmosome: showing desmoplakins (DP), desmogleins (DG) and intermediate filament (IF) accumulation.

DP

DG

IF

IF

D

Adhesion Belt: (AB) Intracellular and intercellular attachment proteins visible.

E

Figure 4 – Permeability of the monolayer to bacteria

• The monolayer is impermeable to non-invasive bacteria (E. coli DH5α) (A).

• The N. meningitidis strain MC58, on the other hand is able to penetrate the monolayer (B).

BA DH5α Infection MC58 Infection

Figure 5 – Translocation mutants

siaD::ery/wt

7-8h 24-25h

0.0

0.5

1.0

1.5

2.0

CI

BA

• Competitive infections, comparing wt N. meningitidis with a capsule mutant (ΔsiaD) (A) and a pilus mutant (ΔpilE) (B). Both mutants show a defect for traversal of the monolayer compared to wt, but the capsule mutant’s defect is greater (average CI after 24hrs of 0.01 compared to for the 0.37 pilus mutant).

Pathogenesis of Neisseria meningitidis

Colonisation of the

nasopharynx

Translocation across

Nasopharyngeal Epithelium

Meningococcal

septicaemia

Translocation across blood-brain barrier

Meningitis

• Gram-negative diplococci, harmlessly colonises the nasopharynx of up to 40% of the population1.

• Adherence and colonisation is type IV pilus dependant2 but pathway for translocation across the nasopharyngeal epithelium is unknown.

• Understanding translocation is vital to understanding the disease process.

• Current studies limited to expensive, technical tissue explants and culture of cells on impermeable substrates.

• The human bronchial epithelial cell line ‘Calu-3’ can be grown into a differentiated epithelium, and has been much used in aerosol medicine studies3, however, it has never been used to study N. meningitidis.Aim• Establish a physiologically relevant cell culture model of the upper respiratory epithelium and use it to investigate translocation of N. meningitidis.

Method Apical Chamber

Basal Chamber

Calu-3 cellsPorous membrane (1μm pore size)

Well of cell culture plate

Cell culture insert

• Cells are grown on inserts in cell culture plates. This creates basal and apical chambers separated by the differentiated epithelium. Translocation can be analysed by infecting the apical chamber and monitoring the passage of bacteria to the basal chamber.

Conclusions• N. meningitidis can infect Calu-3 cells in a manner consistent with other cell lines used in the field.

• A protocol to grow Calu-3 cells on cell culture inserts to form a polarised, differentiated, epithelial monolayers has been optimised.

• The epithelial monolayers are impermeable to non-invasive bacteria and generate trans-epithelial electrical resistance (TEER) showing that they are confluent and not ‘leaky’. Invasive N. meningitidis is able to penetrate the monolayers.

• The pilus mutant shows a competitive disadvantage for translocation compared to wt, a result consistent with a previous study performed in polarised intestinal epithelial cells4.

• We show for the first time that the capsule mutant has massive translocation defect compared to wt. Previous work has shown that the capsule is essential for intracellular survival5. These data suggest N. meningitidis translocates across the epithelium via an intracellular, rather than paracellular, route.

• Future work will involve use of the model to understand the host and pathogen roles in the translocation process.References1. K. A. Cartwright et al., Epidemiol. Infect. 99: 591 (1987).

2. X. Nassif, C. Pujol, P. Morand, E. Eugene, Mol. Microbiol. 32: 1124 (1999).

3. K. Foster, M. Avery, M. Yazdanian, K. Audus, Int. J. Pharm. 208: 1 (2000).

4. C. Pujol, E. Eugene, L. de Saint Martin & X. Nassif, Infect. Immun. 65: 4836 (1997).

5. M. Spinosa, C. Progida, A. Tala, L. Cogli, P. Alifano, C. Bucci, Infect. Immun. 75:3594 (2007).

AcknowledgementsSpecial thanks must go to Mike Hollinshead from the Henry Wellcome imaging suite on the St Mary’s Campus for all his help with the Transmission Electron Microscopy.

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