Expression of Opacity Proteins Interferes with the Transmigration of Neisseria gonorrhoeae across Polarized Epithelial Cells

Abstract

Neisseria gonorrhoeae (GC) establishes infection at the mucosal surface of the human genital tract, most of which is lined with polarized epithelial cells. GC can cause localized as well as disseminated infections, leading to various complications. GC constantly change their surface structures via phase and antigenic variation, which has been implicated as a means for GC to establish infection at various anatomic locations of male and female genital tracks. However, the exact contribution of each surface molecule to bacterial infectivity remains elusive due to their phase variation. Using a GC derivative that is genetically devoid of all opa genes (MS11∆Opa), this study shows that Opa expression interferes with GC transmigration across polarized human epithelial cells. MS11∆Opa transmigrates across polarized epithelial cells much faster and to a greater extent than MS11Opa+, while adhering at a similar level as MS11Opa+. When MS11Opa+, able to phase vary Opa expression, was inoculated, only those bacteria that turn off Opa expression transmigrate across the polarized epithelial monolayer. Similar to bacteria alone or co-cultured with non-polarized epithelial cells, MS11∆Opa fails to form large microcolonies at the apical surface of polarized epithelial cells. Apical inoculation of MS11Opa+, but not MS11∆Opa, induces the recruitment of the Opa host-cell receptor carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) to the apical junction and the vicinity of bacterial adherent sites. Our results suggest that Opa expression limits gonococcal ability to invade into subepithelial tissues by forming tight interactions with neighboring bacteria and by inducing CEACAM redistribution to cell junctions.

Fig 1. Opa expression changes gonococcal interaction with polarized epithelial cells.

Polarized T84 cells on transwells were incubated with or without GC MS11Opa+, MS11ΔOpa, and MS11OpaH for 4 h. Cells were fixed, permeabilized, stained for the junctional protein ZO-1 and gonococci, and analyzed using a confocal microscope. Images shown are representative images from three independent experiments. Scale bar, 5 µm.

Fig 2. Opa expression alters GC-induced redistribution of CEACAM at the apical surface.

Polarized T84 cells on transwells were incubated with GC MS11OpaH and MS11ΔOpa for 4 h. Cells were fixed, permeabilized, stained for the junctional protein ZO-1, gonococci and CEACAM1, and z-series images were acquired using a confocal microscope. Three z-series images at the apical surface were merged (A). Scale bar, 5 µm. Big arrows, big GC aggregates; and small arrows, small GC aggregates. The percentage of GC clusters with CEACAM patches in the vicinity was determined (B). The Pearson correlation coefficient between CEACAM and ZO1 staining was determined using NIH ImageJ software (C). Shown are representative images and the average values from three or four independent experiments. *p = 0.05. ***p = 0.001.

Fig 3. Opa expression reduces the kinetics and magnitude of GC transmigration.

(A-C) Polarized T84 cells grown on transwells were incubated with GC apically at a MOI of 10:1 for varying periods of times. The basolateral media were plated onto GCK to enumerate the number of GC that transmigrated into the basolateral media (A and C). Epithelial cells were lysed and plated to determine the number of adhered GC (B). Shown is the average CFU per transwell (A-B) or the average percentage of transmigrated GC over total epithelial-associated GC (C) from three independent experiments, each of which performed in triplicate. *p< 0.05. (D) The cells were fixed and stained for GC and ZO1. Images of z-series were acquired using a confocal microscope. Shown are xy images at the apical junction areas (top) and xz images from 3D reconstitution across both apical and basolateral surfaces (bottom) from three independent experiments. Scale bar, 10 μm. (E) The cells were processed for transmission electronic microscopy. Arrows, GC. Scale bar, 2 μm.

Fig 4. Only Opa- GC can transmigrate across the polarized epithelial monolayer.

Polarized T84 cells on transwells were incubated with GC apically at a MOI of 10 for 6 h. The basolateral media were collected. T84 cells were washed and lysed to release cell-associated GC. The inoculum (A), cell lysates (B, adhered) and the basolateral media (C, transmigrated) were culture on GCK plates. CFU were determined. Opa expression of the GC colonies were determined using light microscopy (A and B) or colony blotting based on their binding activity to Mab 4B12. Shown were the average data from three independent experiments each with triplicate samples. **p<0.005, ***p< 0.001.

Fig 5. Opa expression has no impact on the permeability of polarized epithelial monolayer infected with GC.

Polarized T84 cells were apically incubated with GC for 6 h in the presence of 1 μg/ml of FITC or HRP in the apical medium. The fluorescence intensity of FITC in the basolateral media was measured at 490 nm using a fluorimeter. The enzymatic activity of HRP was measured using a color changing substrate. Shown are the average percent of FITC and HRP leaked into the basolateral media from three independent experiments.