Description
Disentangle when innate immune memory is adaptive compensation versus a driver of chronic inflammatory damage in aging. Boundary domains: innate-immunity, metabolism. Representative papers: Immunology of Aging: the Birth of Inflammaging.; Human Inflammaging.; Metabolic dysregulation of trained immunity in immune aging and the impact of dietary patterns.
Evidence summary
Trained immunity refers to the epigenetic and metabolic reprogramming of innate immune cells—monocytes, macrophages, NK cells—following an initial stimulus, enabling enhanced responses to subsequent challenges. This form of innate immune memory, mediated by histone modifications (H3K4me1/3, H3K27ac) and metabolic rewiring toward aerobic glycolysis and glutamine catabolism, is distinct from adaptive immune memory (Defining trained immunity and its role in health and disease, Nature Reviews Immunology 2020). In aging, dysregulation of trained immunity is emerging as a critical driver of inflammaging—the chronic, low-grade sterile inflammation characteristic of old age characterized by elevated IL-6, TNF-α, and CRP. Monocytes from older adults display baseline epigenetic “pre-training” signatures that amplify inflammatory outputs while impairing antimicrobial responses, a phenomenon coined inflammaging (The Birth of Inflammaging, Clinical Reviews in Allergy and Immunology 2023; Human Inflammaging, Interdisciplinary Topics in Gerontology 2019).
The fundamental gap is disentangling when innate immune memory serves as adaptive compensation versus acting as a driver of chronic inflammatory damage in aging. BCG vaccination induces trained immunity that protects against heterologous infections, and has been proposed as a strategy to overcome immune dysfunction in elderly populations (Overcoming immune dysfunction in the elderly via trained immunity, International Immunology 2020). However, the same epigenetic reprogramming may amplify baseline inflammatory tone in aged individuals, worsening inflammaging. A 2025 study on metabolic dysregulation of trained immunity in immune aging (American Journal of Physiology: Cell Physiology 2025) is beginning to map how age-associated metabolic changes—altered itaconate, succinate, and fumarate signaling—distort epigenetic reprogramming in monocyte precursors, potentially explaining why trained immunity becomes maladaptive with age.
Recent studies have identified NLRP3 inflammasome activation, oxidized LDL, and advanced glycation end-products as inducers of maladaptive trained immunity in aging macrophages. Emerging strategies targeting epigenetic “erasers” (HDAC inhibitors, DNMT inhibitors) or metabolic checkpoints (itaconate analogs, dimethyl fumarate) offer potential to reset aberrant innate immune memory. However, the therapeutic challenge is to distinguish and selectively modulate the maladaptive trained immunity signatures from protective trained immunity responses without uniformly suppressing innate immune priming, requiring fine-grained epigenomic and metabolomic characterization of aged innate immune cells.