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The interaction of lipopolysaccharide with membrane receptors on macrophages pre-treated with extract of Reishi polysaccharides measured by optical tweezers

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Abstract

Abstract

Lipopolysaccharide (LPS), one of the cell wall components of Gram-negative bacteria, is recognized by and interacted with receptors on macrophages. In this paper, we report the trapping of LPS-coated polystyrene particles via optical tweezers and measured its interaction with murine macrophages (J774A.1 cells) for cells pre-treated with extract of Reishi polysaccharides (EORP) vs. those without EORP treatment. Our experimental results indicate that the cellular affinity for LPS increases when the macrophage is pretreated with EORP. We demonstrate for the first time by conventional biological methods and by tracking the dynamics of optically-trapped LPS-coated particles interacting with J774A.1 cells, that EORP not only enhances J774A.1 cells surface expression of TLR4 and CD14, two receptors on macrophages, as well as LPS binding and phagocytosis internalization, but also reduces the adhesion time constant and increases the force constant of the binding interaction. The application of optical tweezers allows us to study the effect on a single cell quantitatively in real-time with a spatial resolution ~1µm within a single cell.

©2007 Optical Society of America

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Figures (10)

Fig. 1.
Fig. 1. (a). SEM images (20,000X) of uncoated polystyrene particles, BSA-coated polystyrene particles and LPS-coated polystyrene particles. (b) Result of Western blot indicating the presence of pro-IL-1 where the J774A.1 cells were treated with LPS, LPS-coated, BSA-coated and uncoated polystyrene particles.
Fig. 2.
Fig. 2. A schematic diagram of the experimental setup. HW: half-wave plate; PZ: polarizer; BE: beam expander; SF/BE: spatial filter-beam expander; DM: dichroic mirror; QPD: quadrant photodiode; DAQ: data acquisition system; Hg Lamp: mercury lamp.
Fig. 3.
Fig. 3. The effect of EORP on the phagocytosis of Escherichia coli by murine J774A.1 macrophages measured by flow cytometry; (a) short term (5 minute after feeding); (b) long term (1 hour after feeding). The curves labeled “no E. coli” represent the results when the cells were not fed with E. coli. The rest of the curves were obtained (a) 5 minute and (b) 1 hour after the cells (with vs. without EORP treatment) were fed with E. coli. These data are representative of three independent experiments.
Fig. 4.
Fig. 4. The enhancement of surface expression of CD14 and TLR4 on the cellular membrane of macrophage after EORP treatment; (a) CD14 expression analyzed by confocal microscopy; (b) TLR4 expression analyzed by confocal microscopy; (c) CD14 and TLR4 expression analyzed by flow cytometry. The values represent the percentage of cells with fluorescence intensity (of CD14 or TLR4 expression) higher than the reference fluorescence intensity (indicated by the dotted line). These data are representative of three independent experiments.
Fig. 5.
Fig. 5. Phase contrast and fluorescence Images of LPS-FITC binding on J774A.1 cells analyzed by confocal microscopy; (a) cells pre-treated with EORP; (b) cells pre-treated with EORP followed by incubation with anti-CD14 or anti-TLR4 blocking antibody; (c) cells pre-treated with EORP followed by incubation with cytochalasin D or colchicine. These data are representative of three independent experiments.
Fig. 6.
Fig. 6. The relative position of the particle vs. time for the interaction of a LPS-coated particle with a J774A.1 cell; (a) for cell not treated with EORP; (b) for cell pre-treated with EORP for 24 hours. The exponential time constant “τ” associated with the binding rate, deduced from these data, was approximately τ=4.8 seconds in case (a) and τ=1.2 seconds in case (b).
Fig. 7.
Fig. 7. Inhomogeneous distribution of (a) TLR4, and (b) LPS-coated particles binding on J774A.1 cells membrane.
Fig. 8.
Fig. 8. The force constant k(t) of the binding interactions of a LPS-coated particle on the plasma membrane of a J774A.1 cell pre-treated with EORP for 24 hours and then treated with cytochalasin D for 30 minutes measured as a function of time. The force constant k(t) was deduced from the amplitude “D” and the phase “δ” of the particle oscillation as is prescribed by Eq. (1); (a) The force constant increased from approximately 190 pN/µm to 600 pN/µm in about 60 seconds; (b) The force constant was measured to be approximately 200 pN/µm when the chamber was re-positioned every 10 seconds to track the particle and to keep the particle approximately at the trapping center.
Fig. 9.
Fig. 9. The force constant of the binding interaction of a LPS-coated particle on the plasma membrane of a J774A.1 cell pre-treated with paraformaldehyde measured by optical forced oscillation; the left bar for (control) J774A.1 cell without EORP treatment, and the right bar for J774A.1 cell pre-treated with EORP for 24 hours. The data in the control case on the left represent an average over 3 repeated experiments while the data associated with the EORPpretreated cells represent an average over 8 experiments.
Fig. 10.
Fig. 10. LPS-coated particles binding at different location on the membrane of (a) an EORP-pretreated macrophage; (b) an untreated macrophage. The force constant of the binding interaction of a few selected particles measured by oscillatory optical tweezers are also shown in the figure.

Equations (1)

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k ( t ) = k OT ( A cos δ ( t ) D ( t ) 1 )
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