When it comes to staying well, we have a couple of important lines of defense to keep us safe. Our first line of defense is a physical barrier – skin, mucus, and tears that manually prevent bugs from entering our body. Our second line of defense is thanks to our immune system, a complex system that keeps the body functioning at its best
The immune system can be further broken down into two parts – the innate immune system and the adaptive immune system. Let’s break down these two functions of our immunity, and how they work together to keep us feeling well.
The Innate Immune System
The innate immune system is the first to respond if harmful invaders breach our first line of defense. While our skin, mucous membranes, and stomach acid are able to destroy bugs before they get to our immune system, some are still able to get through.
The innate immune system is made up of a few different types of cells, called leukocytes. Leukocytes are also known as white blood cells, and each type has its own function. The leukocytes include, mast cells, phagocytes, macrophage, neutrophils, dendritic cells, basophils and eosinophils, natural killer cells, and T cells. While you don’t need to understand the exact function of each of these cells, know that they are all generally involved in identifying and removing pathogens from the body. 
A quick note on inflammation…
Many of these cells are also involved in the acute inflammatory response. Inflammation is the body’s response to injury or illness. There are two main types of inflammatory response – acute and chronic. Acute inflammation is what many of us have probably experienced at one point or another as a result of a minor injury or infection. When we are injured, the body releases leukocytes that signal the immune system to heal the site of injury or infection. It is the body’s normal, rapid response to promote healing and recovery. Acute inflammation is pretty easy to recognize, and may present as swelling, redness of the skin, or fever.
On the other hand, chronic inflammation has a longer-term effect on our health, and is influenced by a variety of factors including diet, presence of chronic disease, stress, mental health, and lifestyle. This form of inflammation has some more significant long-term effects – the top leading causes of death are all inflammatory conditions, including ischemic heart disease, stroke, cancer, diabetes mellitus, chronic kidney disease, non-alcoholic fatty liver disease, autoimmune, and neurodegenerative conditions. 
In addition to identification and removal of pathogens, as well as the ability to support the acute inflammatory response, some leukocytes are able to communicate with your adaptive immune system, via antigens. Antigens are traces or signals left behind by bad bacteria. The leukocytes use information from antigens to communicate to your adaptive system to enable it to combat the threat more efficiently. Now, let’s review the adaptive immune system and how it helps keep us healthy.
Adaptive Immune System
The adaptive immune system is a bit more complex than the innate immune system. It is our next line of defense in the case that harmful intruders make it past our physical defense line, and the innate defense line.
The adaptive immune system is made up of white blood cells called lymphocytes. There are two lymphocytes that shield against dangerous pathogens, B cells and T cells. B cells create antibodies to identify the invader cells – think of antibodies like a tag that signals the immune system to get rid of these cells. The antibodies fit directly to the antigens on the outside of the cells, triggering your white blood cells to attach to them. T cells, on the other hand, directly attack and destroy foreign invaders. Once defeated, these cells keep a record of the bacteria and how to kill them – this is known as immunization. 
Because all these immune cells are so essential for our daily functioning, it is of the utmost importance to keep them plentiful and healthy. Just like all of the other important systems that keep our bodies running properly, we can support our immune system by leading a healthy lifestyle. Live well, be well!
- Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. Innate Immunity. Available from: https://www.ncbi.nlm.nih.gov/books/NBK26846/
- GBD 2017 Causes of Death Collaborators. Global, regional, and national age-sex-specific mortality for 282 causes of death in 195 countries and territories, 1980-2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet 392, 1736–1788 (2018).
- Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. Chapter 24, The Adaptive Immune System. Available from: https://www.ncbi.nlm.nih.gov/books/NBK21070/
- Carr, Anitra C, and Silvia Maggini. “Vitamin C and Immune Function.” Nutrients vol. 9,11 1211. 3 Nov. 2017, doi:10.3390/nu9111211