The shield against disease: understanding the immune system

• We have not one, but two immune systems 
• Innate and adaptive: a well-oiled machine
• Nutrients that support immune system function

The immune system is the body’s defense system against disease-causing microorganisms, also known as pathogens. This system is made up of many biological processes and structures, and all have a specific job to protect us against disease. 

The immune system has two main subsystems, the innate and adaptive immune systems.

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But who follows their orders?

The innate immune system

The surface of our skin and internal surfaces provide the first physical barrier to potential pathogens.  This is similar to how a moat deters enemies. (2,3)

After breaching this first barrier, the pathogen is met by phagocytes, which make up the bulk of the innate immune system.  Phagocytes are named as such because they destroy pathogens via the process of phagocytosis.  During phagocytosis, the pathogen is engulfed and destroyed using digestive enzymes.

In all battles there are soldiers that are experienced and others who have never wielded a sword in their lives. Similarly, there are two types of phagocytes known as professional or non-professional based upon their effectiveness at phagocytosis.  Only professional phagocytes will be discussed.

Professional phagocytes include many different types of white blood cells. Neutrophils are the first professional phagocyte at the point of infection.  As they are the first responders, they attempt to digest any pathogen they come in contact with. 

Macrophages are another type of phagocyte.  After digesting and destroying the pathogens, the macrophage’s cell surface displays an antigen that the pathogen possessed.  This antigen is seen by T cells, stimulating the action of the adaptive immune system. (4)

Within the innate immune system is the complement system.  This functions as an alarm to the immune system.  The complement system is responsible for marking the pathogens, making them more susceptible to phagocytes, dissolving bacteria cell walls, directly fighting viruses and gathering other immune cells in the blood to assist in the defence. (5)

Natural killer cells (NK) are another type of phagocyte in the innate immune system.  NK cells work by releasing chemicals to promote pathogenic cell death. (6)

The adaptive immune system

If the innate immune system cannot destroy the pathogens, the adaptive immune response is triggered.

The adaptive immune system resembles a neighboring ally, a secondary force which only joins the attack when the innate immune system has been exhausted and unsuccessful in eliminating the pathogen.

The aforementioned T cells are the first cells involved in the adaptive immune response.  They are located in lymph nodes and activated via macrophages presenting with antigens.  Upon activation, T cells can go down two paths.  One is to become a Cytotoxic T-Cell, becoming toxic to all living cells displaying the particular antigen.  The second is to become a T helper cell, enhancing the immune response by activating B cells, NK cells and macrophages. 

B cells are designed to identify and phagocytose cells presenting with the specific antigens.  B cells retain this antigen and present it to helper T cells, causing the B cell to become a plasma cell or memory B cell.

The memory B cell is what gives the adaptive immune system its speed in future infections.  By remembering certain pathogens, they are able to trigger the use of the specific antibody used to kill the pathogen. Plasma cells work in tandem with memory B cells, secreting the specific antibodies.

Antibodies have three main roles in the body.

• To neutralise the pathogen by binding to it via the antigen. This prevents the pathogen from attacking cells.
• To promote phagocytosis by binding to the pathogen, helping phagocytes to recognize it and destroy them.
• To cause the pathogenic cell to burst and die. (7,8)

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Can these castle defences be upgraded?

There are some simple ways to help your immune system fight the battle against microbes.

Lactoferrin

Firstly, Lactoferrin, a multifunctional protein, has a number of benefits to the immune system, such as;

• Co-ordinates the communication between the innate immune system and the adaptive immune system
• An immune modulator, preventing an excessive or incompetent immune response
• Reduces oxidative stress
• Has antibacterial, antifungal and antiviral abilities (9)

Lactoferrin was originally only sourced from human breast milk, however, advances have led to bovine lactoferrin and human recombinant lactoferrin to become available commercially in food and clinical products.

One such source of bovine lactoferrin is undenatured, native whey protein. When undenatured, whey protein contains lactoferrin with its structure maintained, making it quite bioavailable. (10)

Vitamin C

Secondly, vitamin C is a powerful antioxidant that has known advantages to the immune system, including;

• Supporting the barrier provided by internal surfaces of the body against pathogens
• Enhancing phagocytosis, which consequently increases microbial death
• As an antioxidant it protects your cells from damage caused by free radicals from pathogens

Vitamin C, as we know, is found in many different fruits and vegetables.  Additionally, there are supplements containing vitamin C on the market which can aid in increasing vitamin C intake. (11,12)

Selenium

Finally, selenium is an essential nutrient, playing a crucial role in the body. Used to produce selenoproteins, selenium contributes to the following:

• Protection against oxidative damage
• Prevents damage to lipid structures
• Prevents excessive blood clotting
• Reduces inflammation (13,14)

Knowing how the immune system works and the support it needs to defend the castle, it would be wise to consider regular intake of good sources of these compounds, or smart supplementation with food-based products that contain these protective ingredients.

References

1. Chinen, J., Fleisher, T. A., & Shearer, W. T. (2013). Adaptive Immunity. Middleton’s Allergy: Principles and Practice: Eighth Edition, 1–2(2), 20–29.
2. Distefano, M. D. (2015). Functions of the skin microbiota in health and disease James. 25(5), 213–223.
3. Szolnoky, G., Bata-Csörgö, Z., Kenderessy, A. S., Kiss, M., Pivarcsi, A., Novák, Z., … Kemény, L. (2001). A mannose-binding receptor is expressed on human keratinocytes and mediates killing of Candida albicans. Journal of Investigative Dermatology, 117(2), 205–213.
4. Rabinovitch, M. (1995). and Phagocytes: An Introduction. Trends in Cell Biology, 5(March), 85–87.
5. Koegel, L. K., Vernon, T., Koegel, R. L., Koegel, B. L., & Paullin, A. W. (2014). NIH Public Access. 14(4), 220–227.
6. Vivier, E., Tomasello, E., Baratin, M., Walzer, T., & Ugolini, S. (2008). Functions of natural killer cells. Nature Immunology, 9(5), 503–510.
7. Luckheeram, R. V., Zhou, R., Verma, A. D., & Xia, B. (2012). CD4 +T cells: Differentiation and functions. Clinical and Developmental Immunology, 2012.
8. Hoffman, W., Lakkis, F. G., & Chalasani, G. (2016). B cells, antibodies, and more. Clinical Journal of the American Society of Nephrology, 11(1), 137–154.
9. Kellie, T. Al-Mansour, Z. (2017). Chapter Four - Overview of the Immune System. Micro and Nanotechnology in Vaccine Development. 63-81.
10. Siqueiros-Cendón, T., Arévalo-Gallegos, S., Iglesias-Figueroa, B. F., García-Montoya, I. A., Salazar-Martínez, J., & Rascón-Cruz, Q. (2014). Immunomodulatory effects of lactoferrin. Acta Pharmacologica Sinica, 35(5), 557–566.
11. Actor, J. K., Hwang, S.-A., & Kruzel, M. L. (2009). Lactoferrin as a natural immune modulator. Current Pharmaceutical Design, 15(17), 1956–1973.
12. Carr, A.C. Maggini, S. (2017). Vitamin C and immune function. Nutrients.
13. Lu, J., & Holmgren, A. (2009). Selenoproteins. Journal of Biological Chemistry, 284(2), 723–727.
14. Rayman, M. P. (2012). Selenium and human health. The Lancet, 379(9822), 1256–1268.