This 2016 review subject was bacterial infections that result in long-lasting memories:
“Virulence factors modify the epigenomic landscape through targeting of host signaling cascades, or chromatin complexes directly. Additionally, some bacterial factors have intrinsic catalytic activity enabling them to directly modify chromatin.
Virus, fungi, and parasites also induce similar processes.
Epigenomic changes are not the only possible marks contributing to epigenetic memory. Every inducible change that is not rapidly reversed has the potential to maintain a lasting effect.
Most studies in this field have been performed in vitro with fully terminally differentiated cells such as epithelial cells. Since in such cell types cell fate is already established and a short lifespan often occurs in vivo, this raises the question of whether such memory would be relevant for these cells. The same can be applied to differentiated innate immune cells, which also have a short lifetime.
Looking at the response of undifferentiated cells such as stem cells appears much more appropriate to further explore the concept of innate immune memory.”
From the Conclusions and Perspectives section:
“The lasting potential of chromatin marks depends not only on the kinetics of the epigenome, but also on the stimulus itself. For example, in contrast to LPS [lipopolysaccharide, the major constituent of the cell wall of Gram-negative bacteria], which is rapidly cleared from the organism, BCG and the anthrax toxin may persist in the host organism.
The lasting epigenomic effect would not be due to memory, but continuous stimulation by persistent pathogens or persistent components.”
This last point emphasized the principle that damaging sources should be addressed. Enduring epigenetic memories may be symptoms rather than causes when toxic conditions persist. One possible reason why therapies that reverse epigenetic changes may not prove to be effective is that these epigenetic memories may not be the only causes of continuing damage.
I downgraded this review’s rating both because it’s behind a paywall, and because the reviewers made this curious statement:
“We apologize to colleagues whose work was not cited here due to reference restrictions.”
Why did the reviewers submit their work to a journal which imposed such restrictions?
“A Lasting Impression: Epigenetic Memory of Bacterial Infections?”