Aging and Degeneration of the Innate Immune System

Much of the discussion of the age-related decline of the immune system that can be found in the Fight Aging! archives is focused on the adaptive immune system. But the innate immune system also becomes damaged and dysfunctional with age. Here is a quick summary of the functional difference between these two components of the immune system:

The immune system protects organisms from infection with layered defenses of increasing specificity. Most simply, physical barriers prevent pathogens such as bacteria and viruses from entering the organism. If a pathogen breaches these barriers, the innate immune system provides an immediate, but non-specific response. Innate immune systems are found in all plants and animals. If pathogens successfully evade the innate response, vertebrates possess a third layer of protection, the adaptive immune system, which is activated by the innate response. Here the immune system adapts its response during an infection to improve its recognition of the pathogen. This improved response is then retained after the pathogen has been eliminated, in the form of an immunological memory, and allows the adaptive immune system to mount faster and stronger attacks each time this pathogen is encountered.

In short, the innate immune system responds the same way to each new attack and wakes the adaptive immune system to action. The adaptive immune system changes in response to new threats and remembers how to respond to old threats. This process of adaptation is in fact what brings that component of the immune system to its knees eventually. But there are different and less well understood mechanisms at work that undermine the innate immune system:

Elderly individuals display increased susceptibility to chronic inflammatory diseases and microbial infections, such as periodontitis and oral aspiration pneumonia. The resurgent interest in innate immunity in the 2000s has been accompanied by parallel studies to understand the impact of aging on the function of the innate immune system, which not only provides first-line defense but is essential for the development of adaptive immunity.

This review summarizes and discusses our current understanding of age-associated molecular alterations in neutrophils and macrophages, key inflammatory phagocytes implicated in both protective and destructive host responses.

The analysis of recent literature suggests that, in advanced age, phagocytes undergo significant changes in signal transduction pathways that may affect their ability to perform antimicrobial functions or regulate the inflammatory response. These abnormalities are expected to contribute to the pathology of oral infection-driven inflammatory diseases in the elderly. Moreover, the elucidation of age-associated defects in the innate immune system will facilitate the development of intervention therapeutic strategies to promote or restore innate immune function and improve the quality of health in old age.

This all ties into research on inflammaging, a term for the characteristic increase in levels of chronic inflammation coupled with a weakened immune system seen in the old. This is the outcome of systematically malfunctioning components of the immune system - which means that once researchers understand why this is happening, it will be possible to intervene and restore an age-damaged immune system to a more youthful state of operation.

ResearchBlogging.orgHajishengallis G (2010). Too Old to Fight? Aging and its Toll on Innate Immunity. Molecular oral microbiology, 25 (1), 25-37 PMID: 20305805