Immune Function as a Determinant of Aging and Longevity

The state of the immune system is an important determinant of aging. With age, immune function both declines in effectiveness and becomes inflammatory. Chronic inflammation accelerates the progression of all of the common age-related diseases. It disrupts tissue maintenance and regeneration, to pick one of many examples. It is likely that a sizable component of variation in aging arises from the differences between individuals in the degree to which the immune system has become damaged and dysfunctional.

Some of this immune aging is a matter of the burden of exposure to more rather than fewer pathogens over a lifetime: persistent infections in particular, such as cytomegalovirus and other herpesviruses, appear to drive immune aging. Some immune aging stems from the atrophy of the thymus, the organ responsible for maturation of T cells. A lesser volume of active thymic tissue means fewer new T cells to take up an effective defense of the body. Some immune aging is due to failure of barriers in the gut, allowing gut bacteria to trigger inflammatory activity. Some immune aging arises from cellular senescence among immune cells, turning them into harmful centers of inflammatory signaling. All of these issues have potential solutions, but, as in all matters related to aging, far too little funding and attention are given to the relevant development programs.

Pro-inflammatory immune responses are our first line of defence against infectious non-self. Inflammation however, has a cost. During the life-history of a human, low-grade inflammation, develops gradually and contributes to the pathogenesis of a range of age-related diseases from leaky gut to neurodegeneration. Conversely, ageing through cell senescence, can influence immune function with the depletion of the pool of naïve T-cells ready to respond to infection making older individuals more vulnerable to viral disease and less responsive to vaccination regimes. This can in turn, influence human lifespan. In the apparent complexity of this dual relationship it is difficult to arrive at a mechanism of causality because cause and consequence are intimately linked.

Compromised intestinal barrier function in humans has been associated with conditions such as Crohn's disease. Changes in the permeability of the mouse gut, which results in "leaky gut" has consequences on health span. In this context, increased age-associated levels of Tumour Necrosis Factor (TNF) have a negative impact on gut permeability and impacts on lifespan while IL-10 knockout mice have (along with their immune defects) increased intestinal permeability and develop early colitis compromising health span and lifespan. In contrast, TNF-deficient mice are protected from age-associated inflammation.

There is now increasing evidence that inflammation regulates ageing. But which tissues contribute to this is less clear. Brain neuroinflammation represents a critical factor contributing to progression of neurodegeneration. NF-κΒ is the major regulator of inflammation and its sustained activation in forebrain neurons elicits a selective inflammatory response accompanied by decreased neuronal survival and impaired learning and memory. More recent experiments of transient NF-κΒ activation in astrocytes (a type of microglia) through a diverse array of inflammatory cues (infection or application of pro-inflammatory cytokines), resulted in non-cell autonomous neurodegeneration. The central position of microglia innate immunity in neurodegeneration and especially in the risk for late on-set Alzheimer's Disease (AD) is exemplified in human genome-wide association studies. Loss of TREM2 has been associated with increased risk of late on-set AD and increased TREM2 expression in mouse microglia had an anti-inflammatory rescuing effect with the downregulation of several pro-inflammatory markers. This ameliorated the neuropathological and behavioural deficits of AD mouse models.

T cells and B cells undergo immune senescence. Senescence is age-dependent and is the driving force for immune ageing. During ageing, both T and B cells will be depleted and the memory B cells, long-lived plasma cells and peripheral T-cells show defects. In addition, the provision by the thymus of naïve T-cells for the adaptation to new pathogens is limited. The mechanisms of these age-related defects are not fully elucidated but reduced autophagy, is a major driving force for immune senescence. In murine T cells, neutrophils and macrophages, autophagy is attenuated during ageing and autophagy-deficient cells display premature ageing traits.

Germ-free mice live almost 100% to 600 days in contrast to their conventionally-reared counterparts that reach this point with a 60% survival probability. In addition, germ free mice do not display age-associated inflammation while their macrophages retain their antimicrobial activity. This indicates that age-associated changes of the microbiota are a significant driver of lifespan where TNF-mediated inflammation acting as an effector of morbidity. Indeed, treatment of mice with anti-TNF antibodies reversed age-associated changes in the microbiota and ameliorated life expectancy. Therefore, reversing these age-related microbiota changes represents a potential strategy for reducing age-associated inflammation and the accompanying morbidity.

Link: https://doi.org/10.1007/s10522-019-09801-w

Comments

@Reason
Immune response to an antigen, a process known as immune tolerance, is essential for the preservation of immune homeostasis, i.e. maintain health and functioning. Two mechanisms that drive immune tolerance are thymus-derived regulatory T cells, the major mediators of central immune tolerance and peripherally derived regulatory T cells function to regulate peripheral immune tolerance.

Autoimmune diseases - At least one of every two Americans over the age of 65 has atherosclerosis. So common that some experts used to think that atherosclerosis was part of the normal ageing process. Atherosclerosis-related diseases account for 85% of all deaths from cardiovascular diseases and 70% of people with diabetes die from cardiovascular diseases, according to Novo Nordisk.

Harvey Lodish of MIT, using red blood cells modified to carry disease-specific antigens, has prevented and alleviated two autoimmune diseases-multiple sclerosis (MS) and type 1 diabetes-in early stage mouse models. http://wi.mit.edu/news/archive/2017/cargo-carrying-red-blood-cells-alleviate-autoimmune-diseases-mice

Obviously the antigen delivered to the liver induced peripherally derived regulatory T cells against multiple sclerosis (MS) and type 1 diabetes. Regulatory T cells inhibit inflammatory T cells. Therefore on altered communication and inflammation, another hallmark of ageing; Harvey Lodish demonstrated therapeutic development to stimulate regenerative capacity for the body's ability to repair itself, in this case with its own regulatory T cells following antigen stimulation.

Posted by: Denis Demarais at March 8th, 2019 1:07 PM

I'm taking "anti-inflammatories" to reduce inflammation and at the same time "immune boosters" to increase immunity. Which will win? Or will they both win?

Blaylock

"Unlike anti-inflammatory drugs, nanocurcumin,
nanoquercetin, and nanoboswellia inhibit virtually
all inflammatory pathways, thus offering greater
anticancer benefits as well as protection against
inflammation-induced diseases."

So cancer is associated with inflammation and the immune system needs to fight cancer? Reduce chronic inflammation...boost the active immune system?

"At least one of every two Americans over the age of 65 has atherosclerosis. So common that some experts used to think that atherosclerosis was part of the normal ageing process. Atherosclerosis-related diseases account for 85% of all deaths from cardiovascular diseases and 70% of people with diabetes die from cardiovascular diseases, according to Novo Nordisk."

Probably low fiber diet related? Check population studies...

Call me confused...

Posted by: bob at March 13th, 2019 4:54 AM

@bob
In biology nothing is simple.

The going assumptions are in the following lines.
If you have chronic inflammation it wears out the stem cells and it increases the risk of cancer in the long term. Reduced or improper immune function cannot clear SC and leads to increased inflammation while at the same time not being enough to clear the pre cancer cells...

Posted by: Cuberat at March 14th, 2019 5:49 AM

Post a comment; thoughtful, considered opinions are valued. Comments incorporating ad hominem attacks, advertising, and other forms of inappropriate behavior are likely to be deleted.

Note that there is a comment feed for those who like to keep up with conversations.