To understand the immune system and aging requires some knowledge about the immune system and its normal functioning. The immune system protects the body from harmful or foreign objects. It is the body’s very own “military brigade” with front-line soldiers and Generals!
These include bacteria, viruses, fungi, cancer cells and other harmful organisms. A healthy immune system makes cells and antibodies that attack and destroy these harmful entities
What is the Normal Function of the Immune System?
The network of biological processes that protect the body against disease is called the immune system. It is made up of two closely interacting systems. These are an “innate” immune system and an “adaptive” immune system which together detect and wage war on a wide variety of pathogens. Various pathogens such as viruses, cancer cells, parasitic worms, and objects such as wood or glass splinters (Wikipedia) can invade or penetrate into the body. Fortunately, the immune system can identify these pathogens from other healthy cells.
One of the first responses to infection is iInflammation but it can also occur without any known cause.
Immune system cells are produced by the thymus gland, the spleen and other organs. They are then carried through the body by the lymph vessels to the lymph nodes where they are stored and released when needed. These system cells are involved in regulating several physiological activities in the body by interacting interacting with the endocrine (reproductive) and nervous systems. Furthermore, they play a key role in the development of the human embryo and help to repair and regenerate tissues.
How Does the Immune System Do its Work?
To make this easy to understand, we will review the sequence of events.
- A virus or other foreign body infiltrates the body
- The first line defense responder warrior cells (called the “innate immune system”) act quickly and aggressively. They send out alerts and instructions to other cells and provoke inflammation to start attacking and destroying the virus.
- The “innate” immune system is also responsible for cleaning up these damaged cells, misfolded proteins and other debris in the body, even when there is no infection to fight.
- Several days after the innate immune response begins, the “adaptive” immune system of the body starts a second wave of attacks against the invader. This attack is more targeted than the first, methodically destroying cells infected by this specific virus with T-cells.
- When a T-cell comes across a foreign pathogen, it sends out a signaling device that allows the T-cell to bind to the active form of vitamin D to attack the pathogen.
- When everything is working correctly, these T cells (associated with Vitamin D) make copies of themselves so that at the height of the infection, the body is swarming with them. At the end of the cleanup, a few of them remain behind in the body to guard against return attacks from the same pathogen.
Weakening of the Immune System – Disorders in Humans
Failures of defense by the body fall into three main categories: immunodeficiency disorders, autoimmune disorders, and hypersensitivity disorders.
1. Immunodeficiency Disorders
Immunodeficiency disorders occur when one or more parts of the immune system are inactive.
Common causes of poor immune function in developed countries are obesity, alcoholism, and drug use, while the most common cause in developing countries is malnutrition resulting from diets lacking sufficient protein.
Furthermore, surgical removal of the thymus gland for whatever reason, results in severe immunodeficiency and a high susceptibility to infection.
2. Autoimmune Disorders
These disorders are typically caused by overactive immune responses where the immune system fails to properly distinguish between the body’s own cells and invading cells, and begins to attack part of the body. Commonly known autoimmune diseases include rheumatoid arthritis, diabetes mellitus type 1, Hashimoto’s thyroiditis and a form of systemic lupus.
3. Hypersensitivity (or Intolerance) Disorders
Undesirable reactions produced by the normally functioning immune system. They include allergies, can overlap with autoimmunity, and develop as an over-reaction of the immune system which may be irritating, uncomfortable, damaging, or sometimes fatal.
Other General Causes of Weakening of the Immune System
Toxins in foods and the environment, poor diet and stress can all contribute to a decline in immune system activity. When your immune system is weakened, your body becomes fatigued and cannot prevent or fight infections
Unstable Oxygen Molecules in the Body: Immune cells can be damaged by unstable oxygen molecules in the body called free radicals, which may be generated in dangerously high numbers by poor nutrition, X-rays, alcohol, cigarette smoke and pollutants.
Sleep and Rest: The immune system is affected by sleep and rest, and sleep deprivation is detrimental to immune function. Furthermore, the immune response to infection may result in changes to the sleep cycle.
Hormones: Hormones may stimulate, suppress, or regulate the immune system. They play an enhanced role in altering the sensitivity of the immune system in younger adults.
Female sex hormones are known to stimulate both adaptive and innate immune responses. Some autoimmune diseases tend to affect women and their onset often coincides with puberty.
In contrast, male sex hormones such as testosterone appear to be immune suppressing.
Other hormones such as the growth hormone, prolactin and Vitamin D appear to regulate the immune system
The Immune System and Aging – What are the Changes?
As you grow older and with each passing decade, there is a diminishing function of your immune system. It does not work as well as it did before. Moreover, the changes that occur in your network of immune cells are quite complex, resulting in an altered environment of immunity. (Aging Immune System NY Times)
The following immune system changes may occur and make the system less functional with age:
The Immune System and Aging Cause Fewer Number of Immune Cells in the Body:
The ability of the immune system to respond to pathogens is diminished in both the young and the elderly, with immune responses beginning to naturally decline at around 50 years of age. The body may heal more slowly because there are fewer immune cells in the body to bring about healing.
Over-Reaction and Increased Inflammation of the Immune System:
Older cells throughout the body are believed to change with age, releasing their own inflammatory substances. As a result, even perfectly healthy 65-year-olds usually have higher levels of immune proteins (cytokines).
Consequently, damaged cells and waste appear to outrun the ability of the aging immune system to clear it. This means that your innate immune system becomes overwhelmed and descends into a constant state of alert. This triggers inflammation in the body while the system is unable to cope with the overwhelm and begins to run out of certain immune cells.
All this inflammation chaos causing an increased state of chronic inflammation is linked to frailty. Older adults with higher levels of it may be more fragile and less mobile. Furthermore, this inflammatory chaos in an aging body makes it harder for messages sent out by the innate immune system to reach their targetsthereby creating a tendency for the immune system to over-react.
The Immune System and Aging Cause Delayed Response in the Body:
The immune system responds more slowly to normal triggers as immune cells diminish in the body. This increases the risk of getting sick. Flu shots or other vaccines may not work as well or protect for as long as expected.
In older adults, the “adaptive” immune system response takes longer to react, while its response efforts are crippled by the presence of inflammatory chaos. These delays mean that the pathogen has already made many copies of itself by the time the adaptive immune system begins to work properly.
To further complicate this situation, there are fewer new copies of T-cells in older adults. This is important because these cells play a key role as they are trained to hunt down cells infected with a specific pathogen as part of the adaptive response.
An autoimmune disorder is a disease in which the immune system mistakenly attacks and destroys healthy body cells and tissues.
Decline in Ability to Detect and Correct Defects:
The ability of the immune system to detect and correct cell defects also declines. This can result in an increased risk of cancer.
The Immune System and Aging – How Can You Reduce Your Risks?
You can strengthen your immune system and reduce your risks as you age by doing the following:
- Get plenty of EXERCISE. Exercise, helps maintain good health by promoting blood circulation and ensuring a plentiful supply of oxygen throughout the body
- EAT HEALTHY FOODS. Good nutrition keeps your immune system strong.
- VITAMINS help strengthen the immune system by neutralizing cell-damaging particles. Vitamins A, D, C, E, B6 and B12 should be taken as recommended by your physician.
- DO NOT SMOKE. Smoking weakens your immune system.
- LIMIT your intake of alcohol.
- Look into safety measures to prevent falls and injuries. A weak immune system can slow healing.
- Get the flu and pneumonia VACCINES, and any other vaccines your health care provider recommends.
The immune system and aging is an important subject for older adults. Scientists who study the aging immune system believe that understanding it will eventually provide a clearer window into how aging and the immune system are linked. This can help explain disease vulnerability, and studies will lead to better strategies for developing vaccines.
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McDevitt MA. Aging and the blood (2017). In: Fillit HM, Rockwood K & Young J, Eds. Brocklehurst’s Textbook of Geriatric Medicine and Gerontology. 8th ed. Philadelphia, PA., Elsevier: Chapter 24.
Tummala MK, Taub DD & Ershler WB. Clinical immunology: immune senescence and the acquired immune deficiency of aging (2017) In: Fillit HM, Rockwood K, Young J, Eds. Brocklehurst’s Textbook of Geriatric Medicine and Gerontology. 8th ed. Philadelphia, PA., Elsevier: Chapter 93.
How the Aging Immune System Makes Older People Vulnerable to Covid-19 (2020) A version of this article appears in print on Sept. 8, 2020, Section D, Page 7 of the New York edition with the headline: Why Older Adults Are Vulnerable to Coronavirus Effect. https://www.nytimes.com/2020/09/08/health/covid-aging-immune-system.html
Aging Changes in Immunity (2020) https://medlineplus.gov/ency/article/004008.htm