Long-term activation of the innate immune system in atherosclerosis.
Efforts to reverse the pathologic consequences of vulnerable plaques are often stymied by the complex treatment resistant pro-inflammatory environment within the plaque. This suggests that pro-atherogenic stimuli, such as LDL cholesterol and high fat diets may impart longer lived signals on (innate) immune cells that persist even after reversing the pro-atherogenic stimuli. Recently, a series of studies challenged the traditional immunological paradigm that innate immune cells cannot display memory characteristics. Epigenetic reprogramming in these myeloid cell subsets, after exposure to certain stimuli, has been shown to alter the expression of genes upon re-exposure. This phenomenon has been termed trained innate immunity or innate immune memory. The changed responses of 'trained' innate immune cells can confer nonspecific protection against secondary infections, suggesting that innate immune memory has likely evolved as an ancient mechanism to protect against pathogens. However, dysregulated processes of immunological imprinting mediated by trained innate immunity may also be detrimental under certain conditions as the resulting exaggerated immune responses could contribute to autoimmune and inflammatory diseases, such as atherosclerosis. Pro-atherogenic stimuli most likely cause epigenetic modifications that persist for prolonged time periods even after the initial stimulus has been removed. In this review we discuss the concept of trained innate immunity in the context of a hyperlipidemic environment and atherosclerosis. According to this idea the epigenome of myeloid (progenitor) cells is presumably modified for prolonged periods of time, which, in turn, could evoke a condition of continuous immune cell over-activation.
Institute of Innate Immunity, University Hospitals Bonn, University of Bonn, Bonn, Germany; Department of Infectious Diseases and Immunology, UMass Medical School, Worcester, MA, USA.
Anette
A
Christ
Department of Internal Medicine, Radboud University Medical Center, Nijmegen, The Netherlands.
Siroon
S
Bekkering
Institute of Innate Immunity, University Hospitals Bonn, University of Bonn, Bonn, Germany; Department of Infectious Diseases and Immunology, UMass Medical School, Worcester, MA, USA; German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany. Electronic address: Eicke.Latz@uni-bonn.de.
Eicke
E
Latz
Department of Internal Medicine, Radboud University Medical Center, Nijmegen, The Netherlands. Electronic address: Niels.Riksen@radboudumc.nl.
Niels P
NP
Riksen
D000818:Animals; D050197:Atherosclerosis / Q000276:immunology*; D042002:Chromatin Assembly and Disassembly; D044127:Epigenesis, Genetic; D006801:Humans; D007107:Immune System; D064789:Immunity, Heterologous; D007113:Immunity, Innate; D007156:Immunologic Memory; D008213:Lymphocyte Activation
Atherosclerosis; Changed dietary components; Epigenetic reprogramming; Hyperlipidemia; Immuno-metabolism; Innate immune memory; Trained innate immunity