Within the human body, there are approximately 37 trillion cells that work every day to maintain their balance. These cells are structurally and functionally arranged in organs that comprise the body’s systems. Those systems, among others, include the musculoskeletal, digestive, and circulatory systems. Each system carries out specific functions required for a healthy and active human body. The “Immune System” in particular, is the combination of cells, tissues, and molecules in charge of protecting humans against external threats [1].
Our bodies are constantly under attack from invading forces (pathogens*). These pathogens, viruses** and bacteria***, must first bypass our initial line of defence. This primary defence line is the innate (natural or native) immunity, which consists of the skin – the largest organ in the body – and mucus membranes. Both the skin and mucus membranes act as mechanical barriers that prevent pathogens from entering the body. Most infectious agents never get past these defences. The few that manage to make it through are engaged by white blood cells, which seek out and target pathogens. The constantly active white blood cells, neutrophils and macrophages, are another important part of the innate immunity that patrol the body. When a white blood cell encounters a pathogen, it wraps itself around the invader and consumes it. This act of “eating” pathogens is known as phagocytosis. Once consumed, the pathogen is destroyed by specialized chambers filled with highly acidic compounds.
In some cases, neutrophils and macrophages may be overwhelmed by pathogens and require assistance. They seek help from T-cells and B-cells, coordinators of the immune response. These cells are also white blood cells, however, they have higher ranks and specialized functions. Their specific functions are initiated by the “call for help” made by neutrophils and macrophages. During the fight, T-cells and B-cells are encouraged to approach the battlefield when neutrophils and macrophages emit signals and present them with digested bits of the invaders (antigens****). This process helps the T-cells and B-cells to identify invaders. Once the invaders are identified, the T- and B-cells begin dividing quickly to increase forces. The B-cells rapidly begin producing antibodies***** that specifically target and neutralize invaders, which helps in phagocytosis [2]. T-cells coordinate the recruitment of more troops and target healthy cells that have been infected by an invader – this causes the infected cells to self-destruct.
Once the infection has been controlled, the number of specific T- and B-cells that recognize the invader reduce, but some cells remain in circulation and document a memory of past infections. The T- and B-cells constitute the “adaptive (specific or acquired) immunity”, a more specialized response to infection. This adaptive immunity retains the memory of past infections, which allows the immune system to respond more quickly and efficiently following an additional infection [3].
All the cells mentioned in this text are greatly involved in an immune response, however, there are a number of additional factors with various special abilities that come together to create a robust system. Some examples of special abilities that the immune system will address are external threats (microbial and parasitic invasion) and internal threats (cancer) [4].
In most cases, the process of getting infected, fighting and surviving the infection, is the required natural process for gaining immunity against a pathogen. Researchers use immune response knowledge to create vaccines that grant immunity against pathogens the body has never encountered. Vaccines deliver the blueprints for the upcoming battle by introducing deconstructed or weak versions of the invaders that can not cause harm.
If you would like to learn more, BioDecoded has published information on how previous vaccines have been created here. Exciting news arrived in 2020 when RNA- and DNA-based vaccines were developed to help the body’s cells manufacture antigens and prevent future infection - more on this here.
What happens if our immune system is not strong enough to fight against infections? How can we help our immune system do its job? We will discuss these ideas in future posts.
*Pathogen - any microorganism that can cause infection and disease.
**Virus - it can be considered a very small and basic life form or an aggregate of molecules that is simpler than a cell. They can be found in the environment or inside living organisms. It has to infect a cell and use its machinery to multiply, since it cannot multiply by itself. Viruses consist of nucleic acids (DNA or RNA), a protein capsid that contains the nucleic acids and, sometimes, an external envelope of lipids. The flu, measles, AIDS and Covid-19, for instance, are caused by viruses.
***Bacteria - microorganisms invisible to the naked eye that consist of a single cell, though they can group together to form colonies or biofilms. Some bacteria are pathogenic and cause disease, like Salmonella enterica, while others are beneficial to our health, like the ones normally found in the guts.
****Antigen - a molecule or substance that is considered foreign to the organism. It can be a toxin, a small part of a microorganism in cases of infection or it can even be a small part of our own body in cases of autoimmune diseases. The antigens stimulate an immune response and the production of antibodies.
*****Antibody - a molecule produced by immune cells that recognizes and binds to another molecule that is foreign to the organism, the antigen. By binding to the antigen, the antibody can tag the foreign molecule for destruction or directly neutralizes it.
__________________
Written by: Diana
Edited by: María and Natasha
BioDecoded is a volunteer group committed to sharing accurate scientific information. If you have any questions about this topic, please comment or send them to our email.
References:
Abbas, A., Pillai, A., Lichtman, A. Basic immunology: functions and disorders of the immune system. 6th ed. Philadelphia: ELSEVIER; 2020. Available at: https://www.elsevier.com/books/basic-immunology/abbas/978-0-323-54943-1
Nicholson, L., The immune system. Essays in Biochemistry: 2016; 60: 275-301. Available at: https://pubmed.ncbi.nlm.nih.gov/27784777/
Yatim, K., Lakkis, F. A brief journey through the Immune System. Clin J Am Soc Nephrol: 2015; 1-8. Available at: https://pubmed.ncbi.nlm.nih.gov/25845377/
Parkin, J. & Cohen, B. An overview of the immune system. Lancet (London, England) 357, 1777–89 (2001). Available at: https://pubmed.ncbi.nlm.nih.gov/11403834/
Comments