What happens to your immune system as you age?

What happens to your immune system as you age?

The immune system performs an invaluable function in protecting the body against harmful stressors from the environment. As we get older our immune system becomes less efficient, which can increase the likelihood of infection, the severity of cold and flu symptoms, reduced wound healing capability, increased inflammation and the likelihood of hypersensitivity reactions and autoimmune conditions.

The immune system

The immune system comprises of the innate and adaptive immune systems. The innate immune system is the immune system that we are born with, and it responds generically to pathogens (bugs). Our skin and the linings of our body systems such as respiratory, digestive and urogenital mucosal linings make up part of the innate immune system, acting as a physical barrier to foreign substances. We also have the protection of chemical barriers, such as stomach acid, which can destroy foreign substances before they gain entry.

When these barriers are penetrated, specialised immune cells detect the breach and release histamine, which initiates the inflammation process – if you think of a time when you cut yourself and the area becomes red, heated and swollen, this is a demonstration of the innate immune system doing its job.  Behind the scenes, this tangible process is activated when the innate immune system secretes molecules (cytokines and chemokines) which attract white blood cells and macrophages to the site of infection to destroy and remove the foreign substance – such as virus or bacteria – from the body. The innate system then hands over to the adaptive immune system to remember that antigen (foreign substance, bacteria or virus), so that the next time you encounter it, the body can rapidly launch a specific immune response.

The adaptive immune system is also known as acquired immunity, as it develops according to your exposure to different pathogens. It takes longer to respond than the innate immune system and so both systems are needed each time you encounter a foreign substance. 

Two categories of white blood cells – T lymphocytes (T cells) and B lymphocytes (B cells) – respond on behalf of the adaptive immune system. B cells engulf antigens, which are broken down and presented on the surface as a signal to the T cells that there is a problem with the cell. 

There are different categories of T cells that are responsible for different responses depending on the type of signal the B cell presents to them:

  • T Helper (CD4) cells secrete molecules which prompt the B cells to multiply and change form into antibody secreting plasma cells. These plasma cells then circulate searching for the specific virus or bacteria. They release antibodies which bind to that antigen, marking them for destruction.
  • Cytotoxic (CD8) T cells identify infected cells, bind to them and release chemicals to destroy them.
  • Memory T cells recognise antigens and quickly replicate and respond to antigens that have already been encountered by the body.

Different aspects of immune system decline through age

Aging reduces the efficiency of the immune system, which generally becomes noticeable from the age of 60. The immune system gradually declines becoming more prone to infectious diseases and cancers, less capable of wound healing, less responsive to vaccinations and more vulnerable to age-related auto-immune disorders, chronic diseases and inflammatory conditions[1].

One of the key reasons is due to a change in the quantity and types of T cells.  Overall, the number of T cells reduces, as the body becomes less capable of production. This means that there are less “naïve” T cells to respond to newly encountered antigens. At the same time, the relative quantity of memory T cells is increased, due to the different antigens that are encountered over a lifetime[2].

Additionally, the ratio of T helper (CD4) cells to cytotoxic (CD8) changes. This ratio shows how strong your immune system is: you want to see more CD4 cells, as they lead the fight against infection. As you age, CD8 cells outnumber CD4 cells, leaving you more vulnerable[2]. 8% of 20–59-year-olds have an inverted CD4/CD8 ratio whilst 16% of 60%-94-year-olds have an inverted CD4/CD8 ratio[2].

Finally, although plasma cells still produce the same volume of antibodies, these antibodies become less able to attach to the antigen. This further increases the severity of bacteria, viruses and other pathogens, as the immune system becomes less capable of fighting them[3].

Together with inflamm-aging – where cellular waste accumulates in cells and causes increased inflammation in the body – these changes are key features of immunosenescence[1].

‘Immunosenescence’ describes the many factors that result in the progressive reduction in the ability of the immune system to launch an effective immune response as you age[1].

Whilst the adaptive immune system becomes less responsive as you age, the innate immune system responds with increased strength and duration. This contributes to increased inflammation and the progression of age-related diseases[4].

As the immune system becomes less responsive, it becomes harder to identify foreign substances from self and this results in an increase in the prevalence of autoimmune conditions as the immune system mistakenly attacks body tissues and organs. 

There are many ways to support our immune system by living a healthy lifestyle and this is particularly important as you age.


Suzy Walsh 

BBA (Hons)., BNat., mNMHNZ 

Registered Naturopath & Medical Herbalist



[1] Aiello, A., Farzaneh, F., Candore, G., Caruso, C., Davinelli, S., Gambino, C. M., Ligotti, M. E., Zareian, N., & Accardi, G. (2019). Immunosenescence and its hallmarks: How to oppose aging strategically? A review of potential options for therapeutic intervention. Frontiers in Immunology10doi: 10.3389/fimmu.2019.02247

[2] McBride, J. A., & Striker, R. (2017). Imbalance in the game of T cells: What can the CD4/CD8 T-cell ratio tell us about HIV and health? PLOS Pathogens13(11), e1006624. doi: 10.1371/journal.ppat.1006624

[3] Delves, P. J. (2021, September 9). Effects of aging on the immune system - Immune disorders - MSD manual consumer version. MSD Manual Consumer Version. https://www.msdmanuals.com/en-nz/home/immune-disorders/biology-of-the-immune-system/effects-of-aging-on-the-immune-system

[4] Weyand, C. M., & Goronzy, J. J. (2016). Aging of the immune system. Mechanisms and therapeutic targets. Annals of the American Thoracic Society13(Supplement_5), S422-S428. doi: 10.1513/annalsats.201602-095aw