Role of Bacterial Lipopolysaccharide in Enhancing Host Immune Response toCandida albicans

Abstract

Human infections involving yeast of the genus Candida often occur in the presence of bacteria, and, as such, it is important to understand how these bacteria influence innate host immunity towards Candida. Dectin-1 is a cell receptor of macrophages for Candida albicans recognition. The aim of this study was to examine dectin-1 expression by monocytes after stimulation with bacterial lipopolysaccharide (LPS), followed by heat-killed C. albicans (HKC). Freshly isolated human peripheral blood monocytes (PBMCs) and human monocytes cell line (THP-1) cells expressed low levels of dectin-1. Stimulation with LPS and GM-CSF/IL-4 was found to increase dectin-1 expression in both CD14+ human PBMC and THP-1 cells. Enhanced dectin-1 expression resulted in increased phagocytosis of Candida. When THP-1 cells were challenged only with HKC, detectable levels of IL-23 were not evident. However, challenge by LPS followed by varying concentrations of HKC resulted in increased IL-23 expression by THP-1 cells in HKC dose-dependent manner. Increased expression of IL-17 by PBMC also occurred after stimulation with Candida and LPS. In conclusion, bacterial LPS induces an enhanced immune response to Candida by immune cells, and this occurs through increasing dectin-1 expression.

Lipopolysaccharide-mediated enhancement of zymosan phagocytosis by RAW 264.7 macrophages is independent of opsonins, laminarin, mannan, and complement receptor 3

“…Similar dose-dependent effects of LPS have been reported for human peripheral blood monocytes' ingestion of C albicans [10] and increased phagocytic efficiency noted for RAW 264.7 cell uptake of E coli in macrophages exposed to lipid A [24]. We also confirmed that macrophage recognition of zymosan was laminarin sensitive in the absence of LPS but laminarin insensitive for LPS-primed cells [22].…”

“…reported to increase Dectin-1 transcription and cell surface expression with associated enhancement of C albicans phagocytosis [10]. Therefore, it seems possible that cell type and method of cell maturation may contribute to differences observed for LPS effects on Dectin-1 expression.…”

“…Of additional note in this latter study, was the observation of enhanced C glabrata phagocytosis by macrophages exposed to LPS in vitro. C albicans phagocytosis is also increased in freshly isolated human peripheral blood monocytes after stimulation with LPS [10].…”

Candida Survival Strategies

“…Nevertheless, fungalebacterial interactions can also be beneficial for C. albicans. Candida albicans can directly react to lipopolysaccharide (LPS) molecules from bacterial cell membranes, which is an important modulator of C. albicans virulence contributing to coinfection of C. albicans and Escherichia coli (Akagawa, Abe, & Yamaguchi, 1995;Bandara, Yau, Watt, Jin, & Samaranayake, 2009;Rogers, Williams, Feng, Lewis, & Wei, 2013). …”

Cellulose alters the expression of nuclear factor kappa B-related genes and Toll-like receptor-related genes in human peripheral blood mononuclear cells

“…However, this type of activation could also have occurred through other MyD88-independent PRRs expressed by the THP1 cells, such as c-type lectins (Rogers, Williams, Feng, Lewis, & Wei, 2013). Unfortunately, there are many c-type lectins and no reporter cells yet to identify their specific ligands.…”