Fig. 2: BCG vaccination induces trained immunity.

BCG vaccination induces trained immunity of monocytes/macrophages, leading to increased epigenetic reprogramming and host defense capabilities. Chromatin rearrangement induces a “trained” state in monocytes, hence enhancing the effectiveness of innate immune response upon exposure to non-specific pathogens (respiratory syncytial virus or yellow fever virus), and inducing the secretion of proinflammatory cytokines, such as IL-6, IL-1β, and TNF-alpha. However, whether this “training process” can prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) needs further validation. H3K4me3: trimethylation of lysine at position 4 on histone 3; H3K9me3: trimethylation of lysine at position 9 on histone 3. Figure was created using BioRender.