Differential response of human monocyte subsets to heterogeneous Pg-LPS Lipid-A structures

Abstract

OBJECTIVES: Porphyromonas gingivalis (Pg) is currently regarded as a key periodontal pathogen. Pg-lipopolysacharide (LPS) displays a remarkable heterogeneity with both tetra-(LPS1435/1449) and penta-acylated (LPS1690) lipid A structures. Pg-LPS heterogeneity accounts for differential immuno-inflammatory response and thereby contributes to periodontal pathogenesis. Monocytes are heterogeneous and can be classified into three different sub-populations. We recently reported the different pro-inflammatory response of total human monocytes to Pg-LPS with heterogeneous lipid-A structures. The present study further investigated the immuno-inflammatory response of three human monocyte subsets to different isoforms of Pg-LPS. METHODS: Three human monocyte subsets viz. CD14++CD16- (classical), CD14++CD16+ (intermediate) and CD14+CD16++ (non-classical) were isolated by FACS sorting. Purified monocyte subsets were then stimulated with 100 ng/ml of Pg-LPS1435 or Pg-LPS1690 for 2 to 24 h, and E. coli LPS served as a positive control. Gene and protein expression of immuno-inflammatory markers in cellular fraction and culture supernatant was analyzed with qPCR and ELISA, respectively. RESULTS: Monocyte subsets displayed markedly different immuno-inflammatory response to the heterogeneous Pg-LPS isoforms. Classical monocytes expressed highest levels of IL-6, IL-8, IL-1β and CCL-3, whereas intermediate monocytes expressed higher levels of IL-10 and GM-CSF in response to Pg-LPS1690 and E. coli LPS with reference to Pg-LPS1435. In contrast, TNF-α expression was the highest in non-classical monocytes. In addition, Pg-LPS1690 significantly up-regulated the expression of IL-6, IL-8 and TNF-α proteins in line with the gene expression profiles. CONCLUSIONS: This pioneering study demonstrates that human monocyte subsets may exhibit differential response to heterogeneous Pg-LPS isoforms, and contribute to the disruption of tissue homeostasis seen in periodontal disease, unravelling a new area of research in periodontology.Further study is required to determine the underlying molecular mechanisms and biological implications.