Conclusion & perspectives
Trained or primed macrophages exhibit immune memory similar to that of adaptive immunity when challenged with secondary triggers. There are two types of macrophage memory, namely, trained and endowed immunity. Trained macrophages acquire memory via epigenetic and metabolic reprogramming, induce trained immunity, and facilitate an altered immune response upon secondary stimulation. Similarly, primed macrophages can acquire memory, which leads to the development of endowed immunity and allogeneic rejection in response to stimulation with the same allogeneic antigen. The discovery of macrophage memory has challenged traditional dogma regarding the limitations of immunological memory and enriched our understanding of macrophage-mediated immune responses. More importantly, unraveling macrophage memory provides a more comprehensive perspective on the pathogenesis of immune-mediated diseases, and may lead to establishing a new class of vaccines and the development of novel immunoprophylactic and therapeutic strategies.