Rhodobacter capsulatus PG Lipopolysaccharide Blocks the Effects of a Lipoteichoic Acid, a Toll-Like Receptor 2 Agonist.

Lipopolysaccharides (LPS) and lipoteichoic acids (LTA) are the major inducers of the inflammatory response of blood cells caused by Gram-negative and some Gram-positive bacteria. CD14 is a common receptor for LPS and LTA that transfers the ligands to TLR4 and TLR2, respectively. In this work, we have demonstrated that the non-toxic LPS from Rhodobacter capsulatus PG blocks the synthesis of pro-inflammatory cytokines during the activation of blood cells by Streptococcus pyogenes LTA through binding to the CD14 receptor, resulting in the signal transduction to TLR2/TLR6 being blocked. The LPS from Rhodobacter capsulatus PG can be considered a prototype for developing preparations to protect blood cells against the LTA of gram-positive bacteria.

The Effect of a Lipopolysaccharide from Rhodobacter capsulatus PG on Inflammation Caused by Various Influenza Strains.

The development of a specific inflammation in mice that had been infected by two influenza virus strains, A/chicken/Kurgan/5/2005 (H5N1) and A/Hamburg/2009 MA (H1N1), was studied. We investigated the effect of a non-toxic lipopolysaccharide from Rhodobacter capsulatus PG on the survival and body weight of the mice, production of IgG antibodies, and the induction of pro- and anti-inflammatory cytokines in blood serum. The administration of the R. capsulatus PG lipopolysaccharide was shown to induce interferon-ß synthesis, both in healthy and influenza A virus-infected mice, and to promote production of antiviral antibodies in the blood of the influenza-infected animals.

Artifacts Arising from Using Leukocytic Fc Receptor Blocking Buffer.

We studied the effects of Human TruStain FcX buffer (Fcγ receptor blocking solution) in experiments on evaluation of TLR4 level with labeled monoclonal antibodies, intracellular immunofluorescent staining of NF-κB p50, and TNF-α synthesis on human isolated monocytes and whole blood cells. The influence of the blocking buffer on the measured parameters should be taken into account and appropriateness of its use in experiments on isolated cells and whole blood should be considered.

Dynamics of Antagonistic Potency of Rhodobacter capsulatus PG Lipopolysaccharide against Endotoxin-Induced Effects.

The dynamics of antagonistic potency of lipopolysaccharide (LPS) isolated from Rhodobacter capsulatus PG on the synthesis of proinflammatory (TNF-α, IL-1ß, IL-8, IL-6, IFN-γ) and antiinflammatory (IL-10, IL-1Ra) cytokines induced by highly stimulatory endotoxins from Escherichia coli or Salmonella enterica have been studied. Using human whole blood, we have shown that R. capsulatus PG LPS inhibited most pronouncedly the endotoxin-induced synthesis of TNF-α, IL-1ß, IL-8, and IL-6 during the first 6 h after endotoxin challenge. Similarly, the endotoxin-induced release of IFN-γ was abolished by R. capsulatus PG LPS as well (24 h). In contrast to the above-mentioned cytokines, the relatively weak antagonistic activity of R. capsulatus PG LPS against endotoxin-triggered production of IL-6 and IL-8 was revealed. Since R. capsulatus PG LPS displays more potent antagonistic activity against deleterious effects of S. enterica LPS than those of E. coli LPS in the cases of such cytokines as IL-1ß (6 and 24 h), IL-6 and IL-8 (4 h), we conclude that the effectiveness of protective action of antagonist is mostly determined by the primary lipid A structure of the employed agonist.

[Effect of growth conditions on electrophysical properties of Rhodobacter capsulatus PG cells].

Electrophysical characteristics of cells of the phototrophic bacterium Rhodobacter capsulatus PG grown in complete Hutner medium in light or dark were found to differ depending on the composition of their lipopolysaccharides (LPS). Under dark cultivation, the cells synthesized LPS with a shortened structure that determined the electrophoretic properties of cell surfaces. The observed decrease in the effective high-frequency electroconductivity of the dark-grown cells is assumed to be due to a decrease in the intracellular K+ concentration resulting from increased permeability of cytoplasmic membranes of the cells grown under these conditions.

[The effect of composition of the core region of Escherichia coli K-12 lipopolysaccharides on the surface properties of cells].

The pH dependences of electrokinetic potentials (EKP) of the cells of two Escherichia coli K-12 strains (D21 and JM 103) with known lipopolysaccharide (LPS) core composition have been determined by the method of microelectrophoresis. At pH 4.6-5.2, the negative surface charge of the cells with Re core LPS was reliably higher. It was shown that the interaction of bacteria with lysozyme results in a decrease of optical density of suspensions due to higher sensitivity of the cells with complete LPS core to hypotonic shock. LPS release from bacterial cell wall depended also on bacterial LPS core composition and increased with LPS core extension. Electrokinetic measurements and the study of the interaction of cells with lysozyme suggest that higher negative surface charge of E. coli JM 103 cells (Re type LPS) is associated with higher quantity and density of LPS packing in the cell wall as compared with the cells of E. coli D21 (Ra type LPS).

[Relations between the chemotype and the cell electrophoretic properties in Rhodobacter capsulatus strains].

The cells of two Rhodobacter capsulatus strains, B10 and PG, and the LPS of their cell walls were studied by electrophysical and biochemical methods. Strain B10 was found to belong to the R chemotype, and strain PG, to the RS chemotype. A relation was revealed between the chemotype of the photosynthesizing bacteria Rhodobacter capsulatus and the electrophoretic properties of their cells.

Effect of chemotype on Escherichia coli interactions with bactericidal proteins.

We studied the effects of bactericidal proteins (lysozyme and lactoferrin) on endotoxin release from cell wall and inhibition of the growth of Escherichia coli colonies of different chemotypes. The structure of LPS core was found to be essential for the mechanisms of the interactions of the studied proteins with the cell wall. Cell viability after contact with cationic proteins is determined not by the amount of released LPS, but by the mechanism of damage to the cell wall.

Use of colorimetric method for evaluation of LPS of different structure.

We studied the possibility of using the colorimetric method with carbocyanin dye for quantitative measurements of LPS of different structure in aqueous solutions. The absorption spectra (intensity and position of absorption peaks) of LPS-carbocyanin complexes depend not only on the presence of polysaccharide fragment in LPS structure, but also on the core structure.

[Effect of environmental factors on the composition of lipopolysaccharides released from the Rhodobacter capsulatus cell wall].

The goal of this study was to compare the environmental factors that determine viability of the gram-negative photosynthesizing bacteria Rhodobacter capsulatus (specifically, light and growth medium composition) and to assess the effect of these factors on the synthesis and composition of lipopolysaccharides released from the cell wall. Depletion of medium resulted in the release of lipopolysaccharides with a truncated polysaccharide fragment. It is concluded that, due to high viability of these bacteria, the main factor that induced lipopolysaccharide release from the cell wall, irrespective of culturing conditions, is cell division rather than cell death.