Comparative Transcriptome Profiles of Human Blood in Response to the Toll-like Receptor 4 Ligands Lipopolysaccharide and Monophosphoryl Lipid A

Liming Luan,Edward R Sherwood,Yin Guo,Julia K Bohannon,Naeem K Patil,Perenlei Enkhbaatar,Benjamin A Fensterheim,Antonio Hernandez,Jingbin Wang,Yaomin Xu,Ryan Stark

doi:10.1038/srep40050

Abstract

Monophosphoryl lipid A (MPLA), a less toxic derivative of lipopolysaccharide (LPS), is employed as a vaccine adjuvant and is under investigation as a non-specific immunomodulator. However, the differential response of human leukocytes to MPLA and LPS has not been well characterized. The goal of this study was to compare the differential transcriptomic response of human blood to LPS and MPLA. Venous blood from human volunteers was stimulated with LPS, MPLA or vehicle. Gene expression was determined using microarray analysis. Among 21,103 probes profiled, 136 and 130 genes were differentially regulated by LPS or MPLA, respectively. Seventy four genes were up-regulated and 9 were down-regulated by both ligands. The remaining genes were differentially induced by either agent. Ingenuity Pathway Analysis predicted that LPS and MPLA share similar upstream regulators and have comparable effects on canonical pathways and cellular functions. However, some pro-inflammatory cytokine and inflammasome-associated transcripts were more strongly induced by LPS. In contrast, only the macrophage-regulating chemokine CCL7 was preferentially up-regulated by MPLA. In conclusion, LPS and MPLA induce similar transcriptional profiles. However, LPS more potently induces pro-inflammatory cytokine and inflammasome-linked transcripts. Thus, MPLA is a less potent activator of the pro-inflammatory response but retains effective immunomodulatory activity.

Highlights

Organ injury that is termed endotoxin shock and mimics many of the alterations present during severe sepsis and septic shock[9,10]
We observed a 1.5-fold increase in IL1B transcript expression after LPS challenge compared to monophosphoryl lipid A (MPLA) and LPS more potently induced expression of NLRP3 mRNA, which further prompted our investigation of inflammasome activation
Our results show that LPS more potently induces intracellular expression of NLRP3, pro-Caspase-1 and pro-IL-1βprotein as well as secretion of IL-1βby isolated peripheral blood mononuclear cells compared to MPLA

Summary

Introduction

Organ injury that is termed endotoxin shock and mimics many of the alterations present during severe sepsis and septic shock[9,10]. Studies from our research group have consistently shown that priming with MPLA augments the innate host response to infection in murine models of sepsis, including CLP-induced bacterial peritonitis and Pseudomonas burn wound infection, leading to improved survival outcomes[19,20,21]. We hypothesized that MPLA, when compared to LPS, is less potent in inducing expression of pro-inflammatory cytokine genes while maintaining potent adjuvant properties and the ability to augment innate antimicrobial immunity. This study enabled us to identify functional attributes of the differentially expressed transcripts and to uncover the interactions among the differentially expressed genes within treatment groups and with other molecules in the IPA database To our knowledge, this is the first study to compare the transcriptomic profiles in human blood challenged with LPS and MPLA. Our findings have significant translational impact, because MPLA is an attractive immunomodulatory agent with application as a vaccine adjuvant and non-specific modifier of innate immune responses to infection

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