Network Topologies and Dynamics Leading to Endotoxin Tolerance and Priming in Innate Immune Cells

TL;DR

This study uses computational modeling to identify network structures in innate immune cells that lead to endotoxin tolerance or priming, revealing key mechanisms and guiding future experiments.

Contribution

It introduces a systematic computational approach to enumerate network topologies responsible for priming and tolerance in innate immune responses.

Findings

Identified three mechanisms for priming: pathway synergy, suppressor deactivation, activator induction.

Discovered one mechanism for tolerance: inhibitor persistence.

Provided test scenarios for experimental validation of immune response mechanisms.

Abstract

The innate immune system, acting as the first line of host defense, senses and adapts to foreign challenges through complex intracellular and intercellular signaling networks. Endotoxin tolerance and priming elicited by macrophages are classic examples of the complex adaptation of innate immune cells. Upon repetitive exposures to different doses of bacterial endotoxin (lipopolysaccharide) or other stimulants, macrophages show either suppressed or augmented inflammatory responses compared to a single exposure to the stimulant. Endotoxin tolerance and priming are critically involved in both immune homeostasis and the pathogenesis of diverse inflammatory diseases. However, the underlying molecular mechanisms are not well understood. By means of a computational search through the parameter space of a coarse-grained three-node network with a two-stage Metropolis sampling approach, we enumerated all the network topologies that can generate priming or tolerance. We discovered three major mechanisms for priming (pathway synergy, suppressor deactivation, activator induction) and one for tolerance (inhibitor persistence). These results not only explain existing experimental observations, but also reveal intriguing test scenarios for future experimental studies to clarify mechanisms of endotoxin priming and tolerance.