Revival of Krebs-Ringer balanced salt solution for the investigation of polymorphonuclear leukocytes and Pseudomonas aeruginosa biofilm interaction

Effects of Pressure, Hypoxia, and Hyperoxia on Neutrophil Granulocytes

Background: The application of normo- and hyperbaric O2 is a common therapy option in various disease patterns. Thereby, the applied O2 affects the whole body, including the blood and its components. This study investigates influences of pressure and oxygen fraction on human blood plasma, nutrient media, and the functions of neutrophil granulocytes (PMNs). Methods: Neutrophil migration, reactive oxygen species (ROS) production, and NETosis were examined by live cell imaging. The treatment of various matrices (Roswell Park Memorial Institute 1640 medium, Dulbecco's Modified Eagle's Medium, H2O, human plasma, and isolated PMNs) with hyperbaric oxygen (HBO) was performed. In addition, the expression of different neutrophil surface epitopes (CD11b, CD62L, CD66b) and the oxidative burst were investigated by flow cytometry (FACS). The application of cold atmospheric plasma (CAP) to normoxic and normobaric culture media served as a positive control. Soluble reaction products such as H2O2, reactive nitrogen species (RNS: NO2- and NO3-), and ROS-dependent dihydrorhodamine oxidation were quantified by fluoro- and colorimetric assay kits. Results: Under normobaric normoxia, PMNs migrate slower and shorter in comparison with normobaric hyper- or hypoxic conditions and hyperbaric hyperoxia. The pressure component has less effect on the migration behavior of PMNs than the O2 concentration. Individual PMN cells produce prolonged ROS at normoxic conditions. PMNs showed increased expression of CD11b in normobaric normoxia, lower expression of CD62L in normobaric normoxia, and lower expression of CD66b after HBO and CAP treatment. Treatment with CAP increased the amount of ROS and RNS in common culture media. Conclusions: Hyperbaric and normobaric O2 influences neutrophil functionality and surface epitopes in a measurable way, which may have an impact on disorders with neutrophil involvement. In the context of hyperbaric experiments, especially high amounts of H2O2 in RPMI after hyperbaric oxygen should be taken into account. Therefore, our data support a critical indication for the use of normobaric and hyperbaric oxygen and conscientious and careful handling of oxygen in everyday clinical practice.

The circRNA_102911/miR-129-5p/SOX6 axis is involved with T lymphocyte immune function in elderly patients with laparoscopic left hepatectomy for hepatolithiasis

The aim of the present study was to investigate the impact of laparoscopic left hepatectomy (LLH) for hepatolithiasis on the T lymphocyte immune changes of elderly patients and to analyze underlying mechanisms of action behind these changes. A total of 164 patients who underwent LLH due to left-sided hepatolithiasis were recruited. In terms of T lymphocyte immune changes, it was found that firstly, the basic quantity of peripheral lymphocytes in the elderly group was significantly lower than that in a younger preoperative group. Secondly, after surgical trauma, the immune function of T lymphocytes had a significant decline and lasted longer when compared with younger patients, which was reflected by the perioperative changes in the T lymphocyte proliferative ability, levels of IL-2 secreted by T lymphocytes and the percentage of CD3⁺/CD4⁺ T lymphocytes in the peripheral blood. Circular RNA (circRNA) 102911 (102911) was upregulated and microRNA (miR)-129-5p was downregulated in CD3⁺/CD4⁺ T lymphocytes from elderly patients with LLH for hepatolithiasis. Furthermore, the overexpression of 102911 inhibited the proliferation of CD3⁺/CD4⁺ T lymphocytes as well as promoting cell apoptosis, with the opposite effects being observed on knockdown of 102911. miR-129-5p is involved in the proliferation and apoptosis of CD3⁺/CD4⁺ T lymphocytes and may be a promising target of 102911. Moreover, SOX6 is a downstream molecule of miR-129-5p. Immune function and number of T lymphocytes decreased significantly after surgical trauma compared to younger patients, and this decline lasted longer in older patients treated with LLH for hepatolithiasis. The 102911/miR-129-5p/SOX6 axis was found to be involved in T lymphocytes immune function, which provided a novel insight for the treatment of elderly patients with hepatolithiasis.

The Extracellular Polysaccharide Matrix of Pseudomonas aeruginosa Biofilms Is a Determinant of Polymorphonuclear Leukocyte Responses

Bacterial biofilms may cause chronic infections due to their ability to evade clearance by the immune system and antibiotics. The persistent biofilms induce a hyperinflammatory state that damages the surrounding host tissue. Knowledge about the components of biofilms that are responsible for provoking the harmful but inefficient immune response is limited. Flagella are known to stimulate the response of polymorphonuclear leukocytes (PMNs) to planktonic solitary bacteria. However, we provide evidence that flagella are not a prerequisite for the response of PMNs to Pseudomonas aeruginosa biofilms. Instead, we found that extracellular matrix polysaccharides in P. aeruginosa biofilms play a role in the response of PMNs toward biofilms. Using a set of P. aeruginosa mutants with the ability to produce a subset of matrix exopolysaccharides, we found that P. aeruginosa biofilms with distinct exopolysaccharide matrix components elicit distinct PMN responses. In particular, the PMNs respond aggressively toward a biofilm matrix consisting of both Psl and alginate exopolysaccharides. These findings are relevant for therapeutic strategies aimed at dampening the collateral damage associated with biofilm-based infections.

Bacterial aggregate size determines phagocytosis efficiency of polymorphonuclear leukocytes

The ability of bacteria to aggregate and form biofilms impairs phagocytosis by polymorphonuclear leukocytes (PMNs). The aim of this study was to examine if the size of aggregates is critical for successful phagocytosis and how bacterial biofilms evade phagocytosis. We investigated the live interaction between PMNs and Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli and Staphylococcus epidermidis using confocal scanning laser microscopy. Aggregate size significantly affected phagocytosis outcome and larger aggregates were less likely to be phagocytized. Aggregates of S. epidermidis were also less likely to be phagocytized than equally-sized aggregates of the other three species. We found that only aggregates of approx. 5 μm diameter or smaller were consistently phagocytosed. We demonstrate that planktonic and aggregated cells of all four species significantly reduced the viability of PMNs after 4 h of incubation. Our results indicate that larger bacterial aggregates are less likely to be phagocytosed by PMNs and we propose that, if the aggregates become too large, circulating PMNs may not be able to phagocytose them quickly enough, which may lead to chronic infection.