Abstract
Plesiomonas shigelloides is a Gram-negative bacterium that is associated with diarrheal disease in humans. Lipopolysaccharide (LPS) is the main surface antigen and virulence factor of this bacterium. The lipid A (LA) moiety of LPS is the main region recognized by target cells of immune system. Here, we evaluated the biological activities of P. shigelloides LA for their abilities to induce the productions of proinflammatory cytokines (TNF-α, IL-1β, and IL-6) by human and murine macrophages [THP-1 macrophages and immortalized murine bone marrow-derived macrophages (iBMDM)]. Four native P. shigelloides LA preparations differing in their phosphoethanolamine (PEtn) substitution, length, number, and saturation of fatty acids were compared with Escherichia coli O55 LA. The bisphosphorylated, hexaacylated, and asymmetric forms of the P. shigelloides and E. coli LA molecules had similar activities in human and murine macrophages, indicating that shortening of the acyl chains in P. shigelloides LA had no effect on its in vitro activities. The PEtn decoration also had no impact on the interaction with the toll-like receptor 4/MD-2 receptor complex. The heptaacylated form of P. shigelloides LA decorated with 16:0 exhibited strong effect on proinflammatory activity, significantly decreasing the levels of all tested cytokines in both murine and human macrophages. Our results revealed that despite the presence of shorter acyl chains and an unsaturated acyl residue (16:1), the bisphosphorylated, hexaacylated, and asymmetric forms of P. shigelloides LA represent highly immunostimulatory structures.
Highlights
Lipopolysaccharide (LPS, an endotoxin), which is the main virulence factor of Gram-negative bacteria, including Plesiomonas shigelloides, is a well-characterized pathogen-associated molecular pattern and a powerful activator of the innate immune response
Natural P. shigelloides lipid A (LA) molecules comprise a mixture of structures that differ in the numbers, lengths, and saturations of their acyl chains, as well as in PEtn substitutions
The ion at m/z 1740.75 was attributed to an asymmetric hexaacylated LA that is bisphosphorylated at O-1 and O-4’ and whose diglucosamine backbone is substituted by two amide-bound (R)-3-hydroxytetradecanoic acids (14:0 [3-(R)-OH]) and four ester-bound fatty acids, as follows: two (R)3-hydroxydodecanoic acids (12:0[3-(R)-OH]), one dodecanoic acid (12:0), and one tetradecanoic acid (14:0)
Summary
Lipopolysaccharide (LPS, an endotoxin), which is the main virulence factor of Gram-negative bacteria, including Plesiomonas shigelloides, is a well-characterized pathogen-associated molecular pattern and a powerful activator of the innate immune response. Shigelloides LA on Cytokines Level by mediating the interaction of LPS with pattern recognition receptors, such as toll-like receptor 4 (TLR4) [1], on monocytes/ macrophages. As a result, signaling pathways are triggered followed by transcription factors activation (e.g., NF-κB) and production of proinflammatory cytokines (e.g., TNF-α, IL-1β, IL-6) that initiate and shape the host’s immune response against the pathogen. In the case of bacteremia caused by Gram-negative bacteria, an excessive response to LPS may lead to sepsis and septic shock [2,3,4]
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