Written by: Maki Palad, M.D.
Reviewed by: Mubashar Rehman, PHD
The immune system acts as our body’s frontline defense that fights against infections. It also captures malignant cells and auto reactive cells — the cells that attack their own. Aging is a natural process and it is characterized by predictable changes in the body and as we age, we become more susceptible to diseases. This decline starts to affect people’s health at the age of 60 years. Although several organ systems in the body, such as the cardiovascular system and immune system, age differently and at a varied rate, the overall functionality determines ‘successful aging’ —a state free from diseases and relative functional impairment.
In this article, we peek into how our immune system ages and some possible ways we can counter it.
Effects of Aging on the Immune System
Immunosenescence is a term that describes the changes in our body’s immune system that occurs as we age. It puts the elderly population at risk for chronic inflammation, malignancy, infections, and autoimmune disorders. The immune system can be divided into innate and adaptive immunity. The innate immune system made up of macrophages, neutrophils, and natural killer cells is the first line of defense and are present at the time of birth. On the other hand, the adaptive immune system that consists of the T and B lymphocytes develops during the lifetime as the individual is exposed to different antigens. Age-related changes that affect the cells of both systems lead to the decline in immunity . However, it is said that aging affects adaptive immunity more.
Dysfunction of the mechanism of innate immunity 
- Epithelial barriers, such as the mucosal lining of the gut, play a role in the host defense. As the person ages, these barriers are disrupted, allowing the invasion of infection causing organisms and a series of damage.
- Macrophages help in the clearance of invading microorganisms. In the elderly immune system, there is a decrease in these macrophages leading to a longer duration of infection and delayed return to function.
- Neutrophils, on the other hand, are not affected by aging but their phagocytic activity(ability to engulf pathogens and kill them) is significantly reduced.
- The elderly immune system has increased levels of cytokines that contribute to immune dysregulation and chronic inflammation. The resulting imbalance causes functional disability and frailty in the elder population.
The Repertoire of adaptive immunity decreases with age
- Bone marrow cells are responsible for the production of T and B lymphocytes. During aging, there is decreased regenerative capacity of the bone marrow and most cells undergo a programmed cell death [1,2,3].
- The thymus is a secondary lymphoid organ that allows the maturation of T lymphocytes. It is most active early in life and continuously declines with age. It is, then, replaced by fatty tissue. Thymic gland involution results in a progressive decrease in the number of T cells available for defense. This involution completes by the age of 40 to 50 .
- B lymphocytes respond by producing immunoglobulins or antibodies that bind to pathogens and fight infection. This ability to produce antibodies, especially when faced with infection, also decreases with age .
The overall functional response of immune cells is affected in normal aging. Some studies show that vaccination in the elder population also resulted in a poor response compared to the younger population, possibly owing to the negative effects of aging on the immune system.
How To Prevent Weakening of the Immune System
There is no stopping to a natural process such as aging.
- Long term moderate exercise: Data suggests that long-term, moderate exercise can improve immune function in older adults. In one small study, individuals aged 61 to 67 years participated in a 40-minutes aerobic exercise three times per week for six months. The finding of this study showed a decrease in inflammatory cytokines compared to individuals in the resistance training group . T lymphocytes and natural killer cells are also said to be transiently elevated during exercise, hence, contributing to the improved immune function in the elderly.
- Adequate nutrition and supplements: Vitamins and minerals are important for normal immune function. Nutritional deficiency is very common in the elderly, necessitating vitamin supplementation. Providing adequate nutrition and vitamins can help boost the immune system.
- Stress management: Chronic stress can speed up immunosenescence. Stress creates a hormonal imbalance that puts off the normal functioning of the immune system. Overall increased well-being and immunocompetence through stress management can delay the aging of the immune system .
- Routine vaccinations: Recommendations for routine vaccination in the older population is beneficial to boost the immune system. Despite the reduced response to vaccination in the older population, specific vaccines to older adults show effectiveness. Vaccines against tetanus, diphtheria, pertussis, influenza, pneumococcal infection, and zoster are relevant to individuals older than 65 years.
- Maintenance medications: Although no pharmacologic therapy is specific to prevent immunosenescence, some are being studied for their possible benefit. Studies show that statins, the drugs used to lower cholesterol in the blood, have an anti-inflammatory and anti-aging effect . Statins exert this action by inhibiting the “telomere shortening”, a step in the programmed cell death in which DNA is damaged after successive divisions. Metformin, a well-known drug for glucose control, is also said to have some anti-aging effects .
The hallmark of a weakening immune system is the propensity for recurrent infections. As we age, unfortunately, our immune system grows old with us. The effects of aging on our immune system are something that we cannot fully reverse; several factors play their role in deterring the overall health profile of an aging individual. A desirable goal would be to delay the aging process and achieve functionality into old age both physically and cognitively.
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