Inflammaging

Definition

"Inflammaging" describes a chronic, sterile, low-grade inflammatory state that progressively develops with advancing age. The term was first coined by Professor Claudio Franceschi and colleagues in 2000 to characterize the paradoxical observation that, while the aged immune system becomes less efficient at fighting infections (immunosenescence), it simultaneously maintains a state of persistent hyper-activation. Unlike acute inflammation, which is a rapid, high-intensity response to injury or infection that resolves once the threat is removed, inflammaging is subtle, sub-clinical, and unresolved. It is characterized by slightly elevated basal levels of pro-inflammatory cytokines such as Interleukin-6 (IL-6), Interleukin-1 beta (IL-1β), and Tumor Necrosis Factor-alpha (TNF-α) in the blood and tissues.[1][2]

Biological context

The etiology of inflammaging is multifactorial, resulting from a complex interplay between the innate immune system and accumulated cellular damage. A central driver is the chronic stimulation of pattern recognition receptors (PRRs), such as Toll-like receptors and the NLRP3 inflammasome.[3]

This stimulation comes from endogenous "danger signals" known as Damage-Associated Molecular Patterns (DAMPs). Major sources of DAMPs include:

• Cellular Debris: Misfolded proteins and cell fragments that are not efficiently cleared due to declining autophagy.[3]
• Mitochondrial Dysfunction: Leakage of mitochondrial DNA (mtDNA) into the cytoplasm, which the cell mistakes for bacterial DNA.[3]
• Senescent Cells: The Senescence-Associated Secretory Phenotype (SASP) releases a continuous stream of inflammatory mediators.[4]
• Gut Dysbiosis: Age-related changes in the gut microbiome and increased intestinal permeability ("leaky gut") allow bacterial products (lipopolysaccharides) to enter circulation, constantly alerting the immune system.[3]

Relevance to ageing research

Inflammaging is now recognized as a convergence point for many mechanisms of ageing and a major risk factor for morbidity and mortality. It acts as a silent engine driving the progression of most age-related diseases. The constant presence of inflammatory mediators can induce insulin resistance (linking to Type 2 diabetes), promote plaque formation in arteries (atherosclerosis), and accelerate bone loss (osteoporosis).[5]

In the nervous system, neuroinflammation is a key component of Alzheimer’s and Parkinson’s disease pathology. Furthermore, inflammaging contributes to "sarcopenia" (muscle wasting) by promoting protein breakdown and inhibiting muscle synthesis. The concept suggests that the rate of ageing is partly determined by the individual's ability to dampen this inflammatory noise; those who can maintain a "youthful" low-inflammatory profile tend to live longer, healthier lives.[5][6]

Evidence status and limitations

The theory of inflammaging is supported by robust epidemiological evidence. Studies of semi-supercentenarians (people aged 105+) have revealed that while they do show some signs of inflammation, effectively balancing this with anti-inflammatory responses is a key predictor of their longevity. Genetic association studies have also identified variants in immune-regulating genes (such as those for IL-6 and IL-10) that correlate with human lifespan.[6][7]

However, the field faces significant challenges in translation. Inflammation is a double-edged sword; it is essential for tissue repair and defense against pathogens. Therefore, blunt therapeutic approaches that broadly suppress the immune system (like high-dose corticosteroids) are often deleterious in the elderly, increasing the risk of infection and cancer. The goal of current research is to identify specific molecular targets—such as the NLRP3 inflammasome or specific SASP components—that can reduce the pathological "background noise" of inflammaging without compromising the acute immune response required for survival. Distinguishing the optimal level of immune activity remains a complex clinical question.[3][7]

References

1. Franceschi, C., et al. (2000). Inflamm-aging: An evolutionary perspective on immunosenescence. https://pubmed.ncbi.nlm.nih.gov/10911963/
2. Franceschi, C., et al. (2017). Inflammaging and human longevity in the omics era. https://pubmed.ncbi.nlm.nih.gov/28038993/
3. Minciullo, P. L., et al. (2016). An update on inflamm-aging: Mechanisms, prevention, and treatment. https://onlinelibrary.wiley.com/doi/10.1155/2016/8426874
4. Xia, X., et al. (2025). Inflammaging: Triggers, molecular mechanisms, and consequences. https://www.frontiersin.org/articles/10.3389/fimmu.2025.1704203/full
5. Franceschi, C., et al. (2018). Inflammaging: A new immune–metabolic viewpoint for age-related diseases. https://www.nature.com/articles/s41574-018-0059-4
6. Franceschi, C., et al. (2007). Inflammaging and anti-inflammaging: A systemic perspective on aging and longevity. https://pmc.ncbi.nlm.nih.gov/articles/PMC7250180/
7. Verdi, S., et al. (2025). Global research trends in inflammaging and neurodegeneration. https://pmc.ncbi.nlm.nih.gov/articles/PMC12018403/