Immunity and Aging Part 3: What happens to your immune system as you age?
Our immune memory or the antibody repertoire against different diseases grows as we age.
Here is a simple example of how it works. We are all born with a small pool of antibodies. When you are exposed to virus A, you experience your first viral infection. Following this encounter you will develop antibodies against virus A. Subsequently you are exposed to virus B, as a result you acquire antibodies against virus B. Now you antibody collection contains antibodies against both virus A and B. Every time a person is exposed to a new pathogen this process is repeated.
Every day we are exposed to many different microbes in the environment, which enhances our antibody repertoire. Hence a newborn contains a smaller antibody repertoire than their parents who has been exposed to many more different pathogens over their lifetime.
However, our immune systems slow down as we age. While you are most certainly exposed to more pathogens with age, our immune systems change as we age affecting its defense function.
As we age our immune memory is lost. The diversity of the ‘memory’ cells that hold information about antibodies decrease as we age, leading to immune memory loss. In addition, the stem cell number is reduced with age. Since the hematopoietic stem cells in the bone marrow are responsible for replenishing the immune system, our capacity to replenish cells in the immune system goes down with age.
Finally changes occur in our DNA with age. These DNA changes can influence the function of stem cells. Studies show that older stem cells are not as robust as young stem cells in terms of their capacity to produce new cells.
Why is immune aging or immune senescence a problem? The following case studies can provide us with much insight into this question.
The first study examining pandemic influenza observed a link between the number of influenza deaths and age. The very young and the very old are much more susceptible and are likely to perish from the flu. What’s more this disease severity correspond well with the robustness of the immune system and its ability to respond to infections with age.
Newborns who have immature immune systems and the elderly with ‘aged’ immune systems are unable to respond to infections with the same robustness of a younger person. As a result both the seasonal and pandemic flus are much more dangerous to people in these specific age groups.
The second study includes COVID19 data from China. Similar to the flu, COVID19 infections were more likely to be lethal to a person over the age of 65. The trend is similar when you examine data from British Columbia. Our elderly population was much more susceptible to COVID19. This could be due to several different factors such as underlying disease conditions or a weakened immune system.
What is important to realize is that ‘immunosenesence’ or the aging of the immune system can dramatically increase the risk of any infection as well as its severity as we grow older.
Continue to Part 4: Can you rejuvenate the immune system?.