Interactions between Innate Immune Memory and the Central Nervous System

BACKGROUND: Traditionally, immunology has assumed the dogma that immunological memory is exclusive to cells of the adaptive immune system. However, over the past decade, evidence has challenged this paradigm by demonstrating that innate immune cells can exhibit adaptive characteristics, resulting in long-term functional changes. After exposure to infections or sterile inflammation, innate immune cells can exhibit either an enhanced or suppressed inflammatory response upon secondary challenge. This de facto immune memory has been termed trained immunity or immune tolerance, respectively. SUMMARY: This review outlines both classical and newly described features of innate immune cells, highlighting the concepts of trained immunity and innate tolerance, along with their underlying molecular mechanisms. We also discuss the implications of innate immune memory in microglia and explore the potential therapeutic approaches for manipulating innate immunity in the context of neurodegenerative disorders. KEY MESSAGES: While trained immunity plays a crucial role in protecting the host against infections, its dysregulation can lead to chronic inflammation, autoimmune diseases, and potentially contribute to the development of neurodegenerative disorders. On the other hand, tolerance can reduce the inflammatory response and promote tissue regeneration but can also result in increased susceptibility to secondary infections. The long lifespan of microglia, coupled with their ability to learn and adapt their response to previously encountered pathogens or stimuli, underscores the potential long-term implications of their innate immune memory for the development of neuropathology.