Wait... How does my immune system actually work ?
Updated: Mar 22, 2021
Your body has a superpower called the immune system!
In wake of the ongoing COVID-19 pandemic, the world has seen a science experiment play out in real-time. People are infected with viruses, such as the common cold and the flu, all the time. On average, it can take about 10 years to develop a vaccine for a virus. In order to understand how vaccines work, you first need to understand your immune system. The immune system is one of the body's most extraordinary elements! Our immune system fights off harmful viruses and other pathogens that are all around us every day. The immune system is separated into two categories: innate immunity and adaptive immunity.
Notes: Definitions are bolded throughout the blog and are listed at the end of the blog. This is only an overview of key factors involved in the immune systems.
The innate immune system is the body's first defense against pathogens entering the body. When your body is introduced to an unfamiliar pathogen (a bacteria, virus, or fungi) an alarm goes off and the body immediately begins to fight the foreign antigens. Antigens are substances that initiate an immune response. There are two types of antigens: foreign and autoantigens. Autoantigens are produced by our bodies and foreign antigens are produced outside of our bodies.
The actions of the innate immune system begin with pattern-recognition receptors (PRRs), which are responsible for mediating the innate immune system. Once a pathogen enters the body, PRRs detect something known as pathogen-associated molecular patterns (PAMPs). The detection of PAMPs initiates an inflammatory response and activates other innate immune defenses.
“ Think of PRRs as a security scanner and PAMPs as a suspicious pattern that leads to extra security forces coming to the area”
Specific cells that play a key role in the innate immune system’s defense against infections are shown in the chart below. Each one of these cells has a different function that protects and defends our bodies from pathogens.
Although the innate immune system has an excellent response, it is a nonspecific response. This means that the body only identifies the fact that there is a foreign substance in the body. The innate immune system does not have the ability to identify the specific virus present. The nonspecific response of the innate immune system helps prevent the disease from spreading further until the adaptive immune system activates. Dendritic cells are the innate immune cells responsible for activating the adaptive immune system.
The adaptive immune system is your body's second and strongest line of defense. T cells and B cells are responsible for carrying out the majority of the activities in the adaptive immune system. Unlike innate immunity, adaptive immunity has a slow and specific response. Adaptive immunity is acquired over your lifetime because the adaptive immune system has a “memory”. You’re probably thinking - a memory? Well, Yes! Let’s talk about how adaptive immunity works…
You may have heard the word antibodies in the news many times over the last year. Antibodies are the proteins that are produced in the presence of antigens. B cells are responsible for producing specific antibodies against viral antigens.
“Think of antibodies as the Avengers. The Avengers only arrive when there are specific villains present…"
When the B cells bind to the viral antigen, a cascade of events is triggered leading to the elimination of the pathogens set forth in our bodies. “Imagine knocking down the first domino that leads to the rest of them falling down”
One of the events triggered is the expansion of B cells. Long-lived plasma cells and B cell memory cells are produced during B cell expansion. These two cells are extremely important because they retain a memory of the viral antigens. Upon reinfection, these cells will neutralize or produce specific antibodies to eliminate the virus quickly!
That's pretty cool right?! This stimulation of immune memory is one of the key components of developing a vaccine. Triggering that adaptive immune response plays a key role in the development of immunity. The CDC defines immunity as the body’s ability to neutralize or destroy a virus with specific antibodies.
If you were exposed to the same antigen again your immune system would be able to fight off antigens faster because your adaptive immune system will produce specific antibodies to protect you from reinfection.
T cells are the second type of cells produced by the adaptive immune system. You can think of T cells as soldiers. There are two major types of T cells, CD4+ helper and CD8+. Okay, this might sound super complicated so let’s simplify this a bit...
“Think of CD4+ helper cells as the medics on a battlefield.” These CD4+ helper cells are responsible for helping B cells expand and helping CD8+ cells activate. “ You can imagine CD8+ cells as the battlefield soldiers that attack, kill the pathogen, or signal other cells to attack.”
Virus-specific CD8+ cells are produced during the first week of infection. CD8+ cells are abundant during the first two weeks after you are infected with a virus. This is a response to your body killing the virus.
The CD8+ cells present during this process are short-lived because the majority of them disappear a few days after your body has terminated the virus. However, a few CD8+ cells remain and these cells become CD8+ memory cells, which remain in your body over your lifetime!
So the immune system is complicated but beautiful! Listed below are the key takes of this blog!
There are two immune systems with different functions: the innate immune system and the adaptive immune system.
The innate immune system is the body’s first, fastest, and nonspecific line of defense against pathogens.
Innate immune cells activate the adaptive immune cells.
The adaptive immune system produces specific antibodies to fight the foreign invaders in our bodies.
A memory of the viral antibody is developed in the adaptive immune system.
The adaptive immune system plays a key role in developing long-term immunity.
Antigens: a substance that is capable of stimulating an immune response
Pathogen: virus, bacteria, or fungi that cause disease
Pattern-recognition receptors (PRRs): receptors that recognize pathogens
Pathogen-associated molecular patterns (PAMPs): structures produced by pathogens
Immunity: the body’s ability to neutralize or destroy a virus with specific antibodies
B Cells. (2020). British Society for Immunology. https://www.immunology.org/public-information/bitesized-immunology/cells/b-cells
Blanchard, N., Salvioni, A., & Robey, E. (2020). Adaptive Immunity. Toxoplasma Gondii, 57–68. https://doi.org/10.1016/B978-0-12-815041-2.00026-8
Cells of the Innate and Adaptive Immune System. (n.d.). [Chart]. https://www.novusbio.com/research-areas/immunology/adaptive-immunity
John Wherry, E., & Masopust, D. (2016). Adaptive Immunity Neutralizing, Eliminating and Remembering for the Next Time. Viral Pathogenesis, 57–68. https://doi.org/10.1016/B978-0-12-800964-2.00005-7
Purtha, W. E., Tedder, T. F., Johnson, S., Bhattacharya, D., & Diamond, M. S. (2011). Memory B cells, but not long-lived plasma cells, possess antigen specificities for viral escape mutant. Journal of Experimental Medicine, 2599–2606. https://doi.org/10.1084/jem.20110740
MacDonald, A. (2017). Antigen vs Antibody – What Are the Differences? Technology Networks. https://www.technologynetworks.com/immunology/articles/antigen-vs-antibody-what-are-the-differences-293550
Molnar, C. (2015, May 14). 12.2 Innate Immunity – Concepts of Biology – 1st Canadian Edition. Pressbooks. https://opentextbc.ca/biology/chapter/12-2-innate-immunity/
Silva-Gomes, S., Decout, A., & Nigou, J. (2014). Pathogen-Associated Molecular Patterns (PAMPs). Encyclopedia of Inflammatory Diseases, 1–16. https://doi.org/10.1007/978-3-0348-0620-6_35-1
Types of Immunity to a Disease | Vaccines and Immunizations | CDC. (2017). CDC. https://www.cdc.gov/vaccines/vac-gen/immunity-types.htm