Figure 2.

Central and peripheral trained innate immunity. Stimuli, including the BCG vaccine, fungal β-glucan, oxLDL or cytokines, such as IL-1, drive metabolic changes that further promote epigenetic modifications in hematopoietic and myeloid progenitors in the bone marrow (central trained immunity) and in mature innate immune cells, including neutrophils and macrophages (peripheral trained immunity). These changes promote the enhanced adaptive response of myelopoiesis to secondary stimuli, which hence results in increased production of trained neutrophils or monocytes that bear enhanced inflammatory preparedness. The induction of trained innate immunity has a protective role against invading pathogens and could be exploited as cancer immunotherapy but may also fuel chronic inflammatory disorders.