Fig. 4
From: Epigenetic regulation of macrophages: from homeostasis maintenance to host defense
Trained immunity and tolerance are associated with epigenetic reprogramming. Macrophages can be trained or tolerized for specific inflammatory stimuli, depending on the type of trigger. In trained immunity, the initial hit induces long-lasting histone marks. In the case of the second hit, H3K27ac and H3K4me3 have already primed the genes, and the expression is enhanced. In contrast, in tolerance, the first stimulation leads to the activation of macrophages, but the removal of the stimulus results in the loss of the activating marks. In addition, suppressive nucleosome remodeling complexes and histone enzymes are involved in the process
