Figure 3.

Innate immune memory programs triggered by acute and chronic inflammation. IIM is a defense mechanism of the body that provides greater protection against secondary insults thanks to epigenetic reprogramming that enables enhanced and/or dampened functionality of cells. In hematopoietic stem cells (HSCs), various IIM programs - trained immunity, priming or tolerance - can be induced depending on the context of the infection. In the bone marrow, the transient pro-inflammatory environment induced by acute stimulation leads to transient activation of HSCs but long-term trained immunity. Conversely, chronic stimulation maintains a pro-inflammatory environment that leads to sustained activation of HSCs and priming. In both cases, IIM leads to enhanced function upon second stimulation, while tolerance shows a dampened response. Although IIM provides clear protection against many secondary insults, it can also have unfavorable consequences for the organism.