Comparison of the immunostimulatory and proinflammatory activities of candidate Gram-positive endotoxins, lipoteichoic acid, peptidoglycan, and lipopeptides, in murine and human cells

Abstract

The role of lipopolysaccharide (LPS) in the pathogenesis of Gram-negative septic shock is well established. The corresponding proinflammatory and immunostimulatory molecule(s) on the Gram-positive bacteria is less well understood, and its identification and characterization would be a key prerequisite in designing specific sequestrants of the Gram-positive endotoxin(s). We report in this paper the comparison of NF-kappaB-, cytokine- and chemokine-inducing activities of the TLR2 ligands, lipoteichoic acid (LTA), peptidoglycan (PGN), and lipopeptides, to LPS, a prototype TLR4 agonist, in murine macrophage cell-lines as well as in human blood. In murine cells, di- and triacyl liopopeptides are equipotent in their NF-kappaB inducing activity relative to LPS, but elicit much lower proinflammatory cytokines. However, both LPS and the lipopeptides potently induce the secretion of a pattern of chemokines that is suggestive of the engagement of a TLR4-independent TRIF pathway. In human blood, although the lipopeptides induce p38 MAP kinase phosphorylation and CD11b upregulation in granulocytes at ng/ml concentrations, they do not elicit proinflammatory cytokine production even at very high doses; LTA, however, activates neutrophils and induces cytokine secretion, although its potency is considerably lower than that of LPS, presumably due to its binding to plasma proteins. We conclude that, in human blood, the pattern of immunostimulation and proinflammatory mediator production elicited by LTA parallels that of LPS.

Local induction of inflammation affects bone formation

“…Considering the important role of TLR receptor signalling in the innate immune response (O'Neill et al, 2013), the direct effects of LPS and LTA on MSC osteogenesis Fiedler et al, 2013) were likely overshadowed by the cytokine response to these mediators in vivo. As such, macrophages produce various cytokines in response to TLR agonists (Finney et al, 2012;Kimbrell et al, 2008;Su et al, 2006). LPS induces an exaggerated secretion of TNF-α, IL-1 and IL-6 in comparison to LTA or TNF-α (Finney et al, 2012;Kimbrell et al, 2008;Sedger et al, 2014;Su et al, 2006;Yarilina et al, 2008).…”

“…As such, macrophages produce various cytokines in response to TLR agonists (Finney et al, 2012;Kimbrell et al, 2008;Su et al, 2006). LPS induces an exaggerated secretion of TNF-α, IL-1 and IL-6 in comparison to LTA or TNF-α (Finney et al, 2012;Kimbrell et al, 2008;Sedger et al, 2014;Su et al, 2006;Yarilina et al, 2008). Of these abovementioned cytokines, TNF-α and IL-6 contribute to bone healing (Gerstenfeld et al, 2003a;Yang et al, 2007) and enhance the osteogenic differentiation of MSCs (Bastidas-Coral et al, 2016;Glass et al, 2011).…”

“…Of these abovementioned cytokines, TNF-α and IL-6 contribute to bone healing (Gerstenfeld et al, 2003a;Yang et al, 2007) and enhance the osteogenic differentiation of MSCs (Bastidas-Coral et al, 2016;Glass et al, 2011). Although the conditioned medium derived from LPSstimulated monocytes has been shown to induce osteoblast differentiation of MSCs without exogenous growth factors (Guihard et al, 2012), LPS-stimulated macrophages can also produce IFN-γ and NO (Finney et al, 2012;Kimbrell et al, 2008). The synergistic effects of IFN-γ and TNF-α may explain the inhibitory effects of LPS on bone induction (Liu et al, 2011;Reinke et al, 2013).…”

“…The synergistic effects of IFN-γ and TNF-α may explain the inhibitory effects of LPS on bone induction (Liu et al, 2011;Reinke et al, 2013). NO production after LPS stimulation may also have an inhibitory effect on osteoblast growth and differentiation, partly through a pro-apoptotic effect (Kimbrell et al, 2008;van't Hof et al, 2001). Macrophages may be targeted to the increase the efficacy of bone substitutes.…”

Innate Immunity and Human Milk MicroRNAs Content: A New Perspective for Premature Newborns

“…Among TLRs, TLR4 is a transmembrane component of the Lipopolysaccharide (LPS) receptor. It also recognizes heat-shock proteins and unsaturated fatty acids such as lipoteichoic acids synthesized by gram-positive bacteria (22,23).…”