Trained immunity mechanisms

This 2021 cell study investigated how inflammatory memory is established, maintained, and recalled:

“Cells retain a memory of inflammation that equips them to react quickly and broadly to diverse secondary stimuli. Temporal, dynamic changes to chromatin accessibility, histone modifications, and transcription factor (TF) binding occur during inflammation, post-resolution, and in memory recall following injury.

Epigenetic records of inflammation have been found in innate immune cells, including macrophages, monocytes, and natural killer cells, as well as CD8+ and regulatory T cells, granulocyte-monocyte progenitors, and long-term hematopoietic stem cells. Inflammatory memory was recently extended to epithelial barrier tissues, which are the first line of defense against infectious pathogens and noxious agents.

Epigenetic memory of an inflammatory experience is rooted in chromatin of a cell via retention of chromatin accessibility, histone marks, and key TFs that endow it with heightened responsiveness to diverse secondary stimuli. AP-1 (activating protein-1) is a collective term referring to transcription factors composed of JUN, FOS, or ATF (activating transcription factor) subunits that bind to a common DNA site.

1-s2.0-S1934590921002861-fx1_lrg

We unearth an essential, unifying role for the general stress-responsive transcription factor FOS, which partners with JUN and cooperates with stimulus-specific STAT3 to establish memory. JUN then remains with other homeostatic factors on memory domains, facilitating rapid FOS re-recruitment and gene re-activation upon diverse secondary challenges.

We offer a comprehensive, potentially universal mechanism behind inflammatory memory and less discriminate recall phenomena with implications for tissue fitness in health and disease:

  1. Stimulus-specific STAT3 and broad stress factor AP1 co-establish memory domains;
  2. Stem cell factors access open memory domains and remain bound after inflammation;
  3. FOS activates open memory domains, enabling secondary responses to diverse stimuli; and
  4. AP1 mediates epigenetic inflammatory memory across cell types, stimuli, and species.”

https://www.sciencedirect.com/science/article/abs/pii/S1934590921002861 “Establishment, maintenance, and recall of inflammatory memory” (not freely available)


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