Bradyrhizobium Lipid A: Immunological Properties and Molecular Basis of Its Binding to the Myeloid Differentiation Protein-2/Toll-Like Receptor 4 Complex

Lipopolysaccharides (LPS) are potent activator of the innate immune response through the binding to the myeloid differentiation protein-2 (MD-2)/toll-like receptor 4 (TLR4) receptor complexes. Although a variety of LPSs have been characterized so far, a detailed molecular description of the structure–activity relationship of the lipid A part has yet to be clarified. Photosynthetic Bradyrhizobium strains, symbiont of Aeschynomene legumes, express distinctive LPSs bearing very long-chain fatty acids with a hopanoid moiety covalently linked to the lipid A region. Here, we investigated the immunological properties of LPSs isolated from Bradyrhizobium strains on both murine and human immune systems. We found that they exhibit a weak agonistic activity and, more interestingly, a potent inhibitory effect on MD-2/TLR4 activation exerted by toxic enterobacterial LPSs. By applying computational modeling techniques, we also furnished a plausible explanation for the Bradyrhizobium LPS inhibitory activity at atomic level, revealing that its uncommon lipid A chemical features could impair the proper formation of the receptorial complex, and/or has a destabilizing effect on the pre-assembled complex itself.

Microscopical and microbiologic characterization of customized titanium abutments after different cleaning procedures

AIM

To assess and characterize pollution micro-particles and bacterial growth on customized titanium abutments after steaming, ultrasonic and plasma cleaning treatments.

MATERIALS AND METHODS

Thirty commercially available implant abutments, after customization, were randomly divided into 3 groups of 10 and cleansed by steam (considered as control group), ultrasonic cleaning (test group 1) and plasma of Argon (test group 2). For all specimens, SEM analysis and EDAX microanalysis were performed to count and characterize pollution micro-particles, both on the abutment surface and implant-abutment connection. For the control and test groups, mean values and standard deviations were calculated for number and density of micro-particles. Statistical differences were determined by one-way ANOVA with Scheffe multiple comparison test. The level of statistical significance was set at P ≤ 0.05. Additional microbiologic analysis was performed to detect bacterial contamination on the abutment surface.

RESULTS

In the control group, the number of micro-particles on average was 117.5, and 14.1, respectively, on the abutment surface and connection. In the test groups, no pollution was revealed on the abutment (average of 1.09 and 1.13 spots, respectively, in test group 1 and test group 2) and connection (1.28 and 1.41, respectively, in test group 1 and test group 2). The analysis of variance (ANOVA) showed a statistically significant difference for all the variables examined. For each variable, at least one of the groups differs from the others. Scheffe multiple comparison test showed that all comparisons for every variables between the control group and both groups are significant, while there were some comparisons between test group 1 and test group 2 that were not significant. EDAX microanalysis identified micro-particles as residual of lubricant mixed with traces of Titanium and other metals. Microbiologic analysis demonstrated the presence of bacterial growth on the abutment surface only in the control group (111.5 ± 11.43 CFU/ml/implant-abutment as mean value). In the test groups, absence of growing microorganisms was found.

CONCLUSIONS

This study confirmed that both plasma and ultrasonic treatments can be beneficially adopted for abutment cleaning process after laboratory technical stages, to supposedly favor soft tissue healing and implant-prosthetic connection stability.