The Immunological Theory of Aging

The immunological theory of aging asserts that the process of human aging is a mild and generalized form of a prolonged autoimmune phenomenon. In other words, aging—which involves a highly complex series of processes—is suspected to be largely controlled by the immune system.

The process of aging is not fully understood in the medical and science communities, and the primary cause has yet to be uncovered, which is where theories like the immunological theory of aging come in.

Older man walking in woods
Aging. Thanasis Zovoilis / Getty Images

Basics of the Theory

As humans age, they experience changes to almost all physiological functions, including those related to the immune system. Medical experts have proven that immune function does indeed decrease with age, which contributes to a whole host of well-known issues among seniors, from increased health risks posed by common infections like a cold or the flu to a greater occurrence of chronic inflammatory diseases, such as gout and some types of arthritis.

While the data suggests that changes in immune system function in the elderly could be a symptom of the aging process, proponents of the immunological theory of aging reverse the relationship. These theorists believe that common symptoms of aging (like chronic disease) are caused by changes in the immune system.

The Aging Immune System

The immune system changes that seem to accompany old age can have a direct impact on a person's longevity. Not only does your immune system protect you against viruses and bacteria, but it also helps identify and remove cancer cells and toxins. As you get older, the potential for these elements to cause damage in your body increases.

This is confirmed. What triggers these changes in immune system function (and how they develop and progress) is not. Research suggests that old-age-related immune system dysfunction, sometimes known as "inflamm-aging," may, at least in part, cause and/or explain some of the known aspects of the aging processes. In fact, chronic inflammation is believed to contribute to a whole host of chronic and terminal diseases from cancer to Alzheimer's disease.

Cellular Changes

The immune system is made up of cells, substances, and organs. The thymus, spleen, tonsils, bone marrow, and lymphatic system produce, store, and transport cells and substances, such as antibodies, interleukins, and interferon.

As you age, critical cells in the immune system decrease in number and become less functional. Those that are of special interest to gerontologists (scientists who study aging) are the class of white blood cells called lymphocytes, which fight invading bacteria and other foreign cells.

Lymphocytes fall into two major classes:

  • B-cells mature in the bone marrow. One of their functions is to secrete antibodies in response to infectious agents or antigens.
  • T-cells develop in the thymus, which shrinks after puberty. There are two subtypes: Cytotoxic T-cells attack infected or damaged cells directly. Helper T-cells produce powerful chemicals, called lymphokines, which mobilize other immune system substances and cells.

While the number of T-cells remains fairly constant as you age, the portion of them that proliferate and function declines. Furthermore, T-cells destroyed by cancer treatments such as chemotherapy and radiation take longer to renew in older people than they do in younger people.

Beyond making you more prone to common viruses and bacterial infections, such immune system changes can have a much greater impact.

Interleukins—of which there are more than 20—serve as messengers, relaying signals that regulate the immune response. Some, like interleukin-6, rise with age, and it is speculated that they interfere with the immune response in some way. Others, like interleukin-2, which stimulates T-cell proliferation, tend to decrease with age.

When it comes to the immunological theory of aging, some research points to increasing immunogenetic diversification of human cells as the culprit, as opposed to the shifting numbers of cells.

The theory holds that this increased diversification or cell mutation in old age may eventually lead to a failure of cell recognition and the breakdown of certain physiological systems, which ultimately triggers autoimmune-like reactions like chronic inflammation.

A Word From Verywell

Scientists continue to discover the complexities of the aging body and the many interdependent and interconnecting genetic, biochemical, and physiological processes involved. As this understanding grows, their findings could lead to better health, less disability, and greater independence in later life, and potentially longer lifespans. 

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