The ABC’s of the Human Immune System
Immunity is your body’s natural protection system, and it carries out two primary functions—defense and tolerance. Your immune system defends against external invaders—think bacteria, viruses, and parasites—and it patrols your body for internal troublemakers, such as cancer cells. It also regulates your level of tolerance to potential environmental triggers, such as allergens (including pollen, bee stings, grasses, wheat, peanuts, soy, and corn).
When your immune system performs these two functions optimally, it helps keep you healthy. However, when your defenses don’t do their job, or your body’s tolerance level is too low or becomes overwhelmed, it makes you more vulnerable to infections, cancer, and autoimmune disorders, as well as increasing your risk for depression, anxiety, and even psychosis.
Your immune system performs its important mission in 4 ways:
- Identifies external invaders or internal cells or tissues that are misbehaving
- Recruits your white blood cells to attack the bad guys
- Tags and decimates external and internal problems
- Remembers invaders and troublemakers in case they return
The 4 Primary Immune System Functions
- against the external environment: If it fails, you get an infection.
- against the internal environment: If it fails, you get cancer.
- against the external environment: If it fails, you get allergies.
- against the internal environment: If it fails, you get an autoimmune disease.
Immune disorders fall into one of 5 categories, all of which impact your brain health/mental health:
1. Immunodeficiency disorders:
These disorders can either be present from birth or result from an illness, such as human immunodeficiency virus (HIV) or acquired autoimmune deficiency syndrome (AIDS), which damages your immune system. People with HIV are twice as likely to experience depression, and they also have an increased risk of anxiety and cognitive disorders, including dementia.
2. Allergies:
When your immune system views neutral environmental “visitors,” such as pollen or pet dander, as enemies, it can lead to allergies, asthma, eczema, or even life-threatening consequences. In a 2018 study including over 186,000 people, those with asthma, hay fever, and eczema were 66% more likely to develop psychiatric disorders compared with those without allergies. And asthma has been shown to increase the risk of dementia by 30%.
3. Cancers of the immune system:
Leukemia and lymphomas are the most common forms of cancer affecting the immune system. Cancer of any kind has long been associated with detrimental changes in emotional health, and research shows that cancer patients are more likely to have a mental health issue than people without the disease. In fact, as many as 25% of cancer patients have clinical depression.
4. Autoimmune disorders:
When your immune system mistakes your own internal tissues for troublemakers and attacks them, it can create an autoimmune disorder. I typically refer to this as “friendly fire.”
5. Persistent infections:
When you experience recurring infections, it may be an indicator of a compromised immune system.
Excerpted from “The End of Mental Illness” by Daniel G. Amen, MD.
At Amen Clinics, our psychiatrists and Integrative and Functional Medicine physicians treat a wide range of conditions and make recommendations for pro-active therapies to enhance or restore the immune system. For more information, speak to a specialist today at 888-288-9834. If all our specialists are busy helping others, you can also schedule a time to talk.




