Quorum Sensing by Monocyte-Derived Populations

Abstract

Quorum sensing is a type of cellular communication that was first described in bacteria, consisting of gene expression regulation in response to changes in cell-population density. Bacteria synthesize and secrete diffusive molecules called autoinducers, which concentration varies accordingly with cell density and can be detected by the producing cells themselves. Once autoinducer concentration reaches a critical threshold, all bacteria within the autoinducer-rich environment react by modifying their genetic expression and adopt a coordinated behavior (e.g., biofilm formation, virulence factor expression, or swarming motility). Recent advances highlight the possibility that such type of communication is not restricted to bacteria, but can exist among other cell types, including immune cells and more specifically monocyte-derived cells (1). For such cells, quorum sensing mechanisms may not only regulate their population size and synchronize their behavior at homeostasis but also alter their activity and function in unexpected ways during immune reactions. Although the nature of immune autoinducers and cellular mechanisms remains to be fully characterized, quorum sensing mechanisms in the immune system challenge our traditional conception of immune cell interactions and likely represent an important mode of communication at homeostasis or during an immune response. In this mini-review, we briefly present the prototypic features of quorum sensing in bacteria and discuss the existing evidence for quorum sensing within the immune system. Mainly, we review quorum sensing mechanisms among monocyte-derived cells, such as the regulation of inflammation by the density of monocyte-derived cells that produce nitric oxide and discuss the relevance of such models in the context of immune-related pathologies.

It’s Not Easy Being Green: A Narrative Review on the Microbiology, Virulence and Therapeutic Prospects of Multidrug-Resistant Pseudomonas aeruginosa

“…The detailed description of these signal molecules is outside of the scope of this review (for details, see References [103][104][105][106][107][108][109][110][111][112][113]). Additionally, these autoinducer molecules are capable of dampening the innate immune response and inducing cytokines and chemokines [114]. As the production of biofilm and the secretion of other virulence factors are all governed by the complex QS system of P. aeruginosa, they have significant influence on the virulence of these bacteria.…”

Deciphering Natural Killer Cell Homeostasis

“…Quorum sensing, which is a form of chemical communication in bacteria whereby sensing of an autoinducer is used to synchronize group behavior, has recently been proposed to also control immune cell homeostasis (77). For example, colony stimulating factor 1 (CSF1) produced by the surrounding stromal cells is proposed to function as the autoinducer in macrophages, whereby uptake of CSF1 controls the rate of proliferation and survival to maintain a steady population density at homeostasis (78).…”

Decidual innate immune cell kinetics following lipopolysaccharide challenge

“…Similarly, Muldoon et al proposed a revised model of Mϕ activation, in which LPS stimuli resulted in either low or high activation states in genetically identical Mϕ culture; this bimodality of LPS-induced Mϕ activation was largely attributed to 'quorum licencing', whereby cell density and external milieu determines a Mϕ's response to inflammatory stimulus [63,64]. We examined gross fetal and placental metrics in the surviving pregnancies.…”