MPLA inhibits release of cytotoxic mediators from human neutrophils while preserving efficient bacterial killing

Abstract

Monophosphoryl lipid A (MPLA) is a lipopolysaccharides (LPS) derivative associated with neutrophil-dependent anti-inflammatory outcomes in animal models of sepsis. Little is known about the effect of MPLA on neutrophil function. This study sought to test the hypothesis that MPLA would reduce release of cytotoxic mediators from neutrophils without impairing bacterial clearance. Neutrophils were isolated from whole blood of healthy volunteers. The effects of MPLA and LPS on autologous serum-opsonised Pseudomonas aeruginosa killing by neutrophils and phagocytosis of autologous serum-opsonised zymosan were examined. Neutrophil oxidative burst, chemotaxis, enzyme and cytokine release as well as Toll-like receptor 4 (TLR4) expression were assessed following exposure to LPS or MPLA. LPS, but not MPLA, induced significant release of superoxide and myeloperoxidase from neutrophils. However, MPLA did not impair neutrophil capacity to ingest microbial particles and kill P. aeruginosa efficiently. MPLA was directly chemotactic for neutrophils, involving TLR4, p38 mitogen-activated protein kinase and tyrosine and alkaline phosphatases. LPS, but not MPLA, impaired N-formyl-methionyl-leucyl phenylalanine-directed migration of neutrophils, increased surface expression of TLR4, increased interleukin-8 release and strongly activated the myeloid differentiation primary response 88 pathway. Phosphoinositide 3-kinase inhibition significantly augmented IL-8 release from MPLA-treated neutrophils. The addition of MPLA to LPS-preincubated neutrophils led to a significant reduction in LPS-mediated superoxide release and TLR4 surface expression. Collectively, these findings suggest that MPLA directs efficient chemotaxis and bacterial killing in human neutrophils without inducing extracellular release of cytotoxic mediators and suggest that MPLA warrants further attention as a potential therapeutic in human sepsis.

Toll-like receptor 4 stimulation with monophosphoryl lipid A ameliorates motor deficits and nigral neurodegeneration triggered by extraneuronal α-synucleinopathy

“…Although a similar extent of reduction of CCL2 and CCL4 brain levels was observed in PLP-α-syn mice treated with LPS, the beneficial effects of LPS were limited due to several reasons. First, LPS treatment caused significant toxic inflammatory response in contrast to MPLA in the PLP-α-syn mouse model, similar to findings reported in other studies [48, 49]. Second, in contrast to MPLA, LPS had a strong effect on the re-distribution from non-toxic soluble monomeric to toxic insoluble oligomeric α-syn species in the brains of PLP-α-syn mice.…”

A cell-based microarray to investigate combinatorial effects of microparticle-encapsulated adjuvants on dendritic cell activation

“…10). IL-10 was also upregulated by each adjuvant individually, as expected, 57,58 with similar responses across adjuvants (Fig. 10b, d and f leftmost points).…”

Revisiting neutrophil responses to toll-like receptor 4 : influence of ligand structures and cellular environments.

“…The weak phagocytosis priming activity of MPLA is consistent with earlier observations (130,132,141). One possible mechanism for such low activity of MPLA could be due to its relative inability to trigger neutrophil granule exocytosis, a process through which primed neutrophils equip their plasma membrane with proteins that assist in phagocytosis and other effector functions (48).…”

“…MPLA influences the responses of human neutrophils (130). In our study of human primary neutrophils, we show that MPLA is very weak at priming phagocytic activity.…”

“…LPS is well known to induce neutrophil degranulation (48,91,130). Neutrophils contain 4 granule subtypes that are enriched in antimicrobial proteins and proteases.…”