Endotoxin, a key component of Gram-negative bacterial membranes, remains a central focus in understanding host–pathogen interactions and immune modulation. In this review, we examine the multifaceted roles of endotoxin, with particular emphasis on how its structural variants modulate host immune recognition and inflammatory signalling. We explore the complex mechanisms by which endotoxin activates innate immune pathways and how these responses evolve under repeated or chronic exposure conditions. Special attention is given to the phenomenon of endotoxin tolerance, an adaptive reprogramming of immune cells that can profoundly alter inflammatory outcomes. While this tolerance serves as a protective mechanism against hyperinflammation, mounting evidence suggests that it may have a “dark side”, potentially impairing immune surveillance and promoting disease states such as cancer. We also discuss emerging clinical and therapeutic strategies that harness or counteract endotoxin-driven responses, from vaccine adjuvants to anti-sepsis interventions. By integrating recent findings from immunology, microbiology, and translational medicine, this review sheds light on the dual nature of endotoxin and its far-reaching implications for human health.

This study sought to elucidate the molecular principles by which bovine lactoferrin (bLF) governs ruthenium(III) coordination and to assess how protein-guided binding translates into structural and biological effects. The protein was modified using potassium aquapentachlororuthenate(III) (K₂[RuCl₅(H₂O)]) as a metal precursor. The obtained LF–Ru systems were comprehensively examined using spectroscopic (spectrofluorimetry, DLS, ATR-FTIR, SRCD), spectrometric (ICP-OES), microscopic (LM, SEM-EDS, TEM-EDS), scattering (SAXS), and electrophoretic (SDS-PAGE) techniques. Antibacterial activity was evaluated for LF and LF–100Ru against Gram-positive (Enterococcus faecalis) and Gram-negative (Escherichia coli, Klebsiella pneumoniae) bacteria. The cellular response to LF–Ru complexes was investigated using murine fibroblast (L929), human hepatocellular carcinoma (HepG2), and human colorectal adenocarcinoma (Caco-2) cell lines. Molecular docking indicated favorable Ru(III) binding in histidine-containing regions related to native metal-binding motifs. Molecular dynamics simulations supported conformational stability upon metal binding, whereas quantum-mechanical calculations on simplified residue models were used only to assess qualitative donor preferences. The adsorption isotherm was better described by the Langmuir model, indicating saturation-like binding of Ru(III) to accessible LF regions at low and moderate loading. At the highest precursor concentrations, BET-style analysis together with TEM observations suggested additional secondary Ru accumulation within the protein matrix. Fluorescence quenching demonstrated strong interactions in the LF–Ru system (K_a = 1.789 × 10⁴ M⁻¹). Desorption studies indicated only minor metal release from LF–100Ru after incubation in simulated gastric and intestinal fluids. Importantly, LF–100Ru reduced the viability of HepG2 and Caco-2 cells while showing comparatively low toxicity toward normal L929 fibroblasts under the tested conditions, indicating a differential cellular response.