LL-37 is the only member of the cathelicidin-type host defense peptide family in humans. It exhibits broad-spectrum bactericidal activity, which represents a distinctive advantage for future therapeutic targets. The presence of choline in the growth medium for bacteria changes the composition and physicochemical properties of their membranes, which affects LL-37’s activity as an antimicrobial agent. In this study, the effect of the LL-37 peptide on the phospholipid monolayers at the liquid–air interface imitating the membranes of Legionella gormanii bacteria was determined. The Langmuir monolayer technique was employed to prepare model membranes composed of individual classes of phospholipids—phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), cardiolipin (CL)—isolated from L. gormanii bacteria supplemented or non-supplemented with exogenous choline. Compression isotherms were obtained for the monolayers with or without the addition of the peptide to the subphase. Then, penetration tests were carried out for the phospholipid monolayers compressed to a surface pressure of 30 mN/m, followed by the insertion of the peptide into the subphase. Changes in the mean molecular area were observed over time. Our findings demonstrate the diversified effect of LL-37 on the phospholipid monolayers, depending on the bacteria growth conditions. The substantial changes in membrane properties due to its interactions with LL-37 enable us to propose a feasible mechanism of peptide action at a molecular level. This can be associated with the stable incorporation of the peptide inside the monolayer or with the disruption of the membrane leading to the removal (desorption) of molecules into the subphase. Understanding the role of antimicrobial peptides is crucial for the design and development of new strategies and routes for combating resistance to conventional antibiotics.

Background/Objectives. The current study explores the impact of CLL on γδ T cells and, in an attempt to better understand the sources of immunosuppression, assesses the impact of M-MDSCs on γδ T cells in vitro. Methods. The study included 163 CLL patients and 34 healthy volunteers. γδ T cells were screened with flow cytometry, including NKG2D, Fas, FasL, and TRAIL staining. Additionally, to deepen understanding of the immunosuppressive impact of CLL on γδ T, a set of in vitro co-cultures of γδ T and M-MDSCs was performed. Results. RNAseq revealed significant, though relatively minor, changes in the transcriptome. Functional analyses showed a minor drop in cytotoxic potential against CLL cells. Finally, depletion of M-MDSCs from CLL-derived peripheral blood mononuclear cells did not restore γδ T cells’ proliferative response. Conclusions. Altogether, this suggests a minor impact of M-MDSCs on activated γδ T. Thus, it seems probable that other mechanisms than M-MDSCs mediate the negative impact of CLL on circulating γδ T cells.

Legionella pneumophila is widely recognized as the principal organism responsible for Legionnaires’ disease. Modifications of surface-exposed lipopolysaccharide in L. pneumophila are key determinants of bacterial adaptation to host cells. Using a mutant strain deficient in N-methylation of legionaminic acid and fluorescence-based biophysical analyses, it was demonstrated that N-methyl groups linked to the acetimidoylamino group of legionaminic acid modulate the physicochemical properties of the bacterial cell surface and influence the interaction of L. pneumophila with macrophages. Loss of N-methyl groups reduced the efficiency of bacterial interaction with THP-1-derived macrophages and impaired intracellular proliferation. In addition, the presence of N-methyl groups in legionaminic acid contributes to increased TNF-α production in THP-1 macrophages stimulated with L. pneumophila sg1 LPS, without affecting IL-6 induction, suggesting that N-methylation of legionaminic acid may skew the early pro-inflammatory response toward TNF-α-dominated signaling during L. pneumophila infection.