The Pathogenesis of ACLF: The Inflammatory Response and Immune Function

Although systemic inflammation is a hallmark of acute-on-chronic liver failure (ACLF), its role in the development of this syndrome is poorly understood. Here the author first summarizes the general principles of the inflammatory response. Inflammation can be triggered by exogenous or endogenous inducers. Important exogenous inducers include bacterial products such as pathogen-associated molecular patterns (PAMPs) and virulence factors. Pathogen-associated molecular patterns elicit inflammation through structural feature recognition (using innate pattern-recognition receptors [PRRs]), whereas virulence factors generally trigger inflammation via functional feature recognition. Endogenous inducers are called danger-associated molecular patterns (DAMPs) and include molecules released by necrotic cells and products of extracellular matrix breakdown. Danger-associated molecular patterns use different PRRs. The purpose of the inflammatory response may differ according to the type of stimulus: The aim of infection-induced inflammation is to decrease pathogen burden, whereas the DAMP-induced inflammation aims to promote tissue repair. An excessive inflammatory response can induce collateral tissue damage (a process called immunopathology). However immunopathology may not be the only mechanism of tissue damage; for example, organ failure can develop because of failed disease tolerance. In this review, the author also discusses how general principles of the inflammatory response can help us to understand the development of ACLF in different contexts: bacterial infection, severe alcoholic hepatitis, and cases in which there is no identifiable trigger.