T Cells, B Cells, DCs, NKs: The Immune Cell Alphabet Soup + Functions

By: Tana Mardian

Our bodies are constantly working to keep us healthy. Whether it be sitting next to a classmate that has a cold, getting a sunburn, or anything in between, our immune system takes over, working to ward off infection and repair any damage. If we do end up getting sick, for example, we might notice big, swollen lymph nodes around our throat and neck. Why do our lymph nodes puff up? You might be wondering, what really goes on in the immune system?

To start off, our immune system has two major components: the innate and adaptive systems. The innate immune system acts quickly, within minutes to hours of encountering a foreign invader. It is nonspecific, meaning that it recognizes general patterns of many pathogens. This defense does not depend on prior exposure to an antigen (any foreign substance that causes your immune system to react) to launch an attack, and it can recognize a wide range of pathogens (Banasik & Copstead, 2019). The main cells involved in this portion of the immune system are natural killer (NK) cells, as well as phagocytic cells like macrophages and neutrophils. The other section of our immune system is the adaptive or specific system. The B and T lymphocytes of this unit work best on their second exposure to an antigen, enabling a specific and effective response (Banasik & Copstead, 2019). These cells have long-lasting memory, which is why vaccines work so well with this system.

The main players in our immune system are leukocytes, or more commonly known as white blood cells (WBCs). Each WBC has a special function in the immune system. When a foreign invader has gotten into the body, macrophages and dendritic cells (DCs) are frequently the first cells to encounter the antigen. They are important messengers, as they let the other immune cells know that something is wrong. Macrophages are phagocytic, meaning they ingest and destroy microbes. While macrophages also participate in antigen presentation, DCs are our major antigen-presenting cells (APCs). This means that, after ingesting the foreign invader, DCs show the antigen to the T cells in our lymph nodes and spleen, initiating a greater immune response (Banasik & Copstead, 2019). 

Additionally, APCs have to use the proper major histocompatibility complex (MHC) to help other immune cells distinguish between host and foreign cells (“Immune Cells,” 2014). For example, intracellular antigens are presented on MHC I complexes. The MHC I could be presenting something like a virus or even cancerous cells. This process will recruit cytotoxic T cells that will destroy the infected cell. MHC II complexes hold extracellular antigens, and this alerts T helper cells, which initiate further immune cell responses. T helper cells might cause the activation of B cells, another essential component of the adaptive immune system (Banasik & Copstead, 2019). 

B cells are most known for their antibody production, something we’ve heard a lot about in preventing infection from COVID-19. The activation of B cells by T cells and the proliferation of antibodies is also what causes our swollen lymph nodes when we’re sick; the immune system is put into overdrive to get rid of the invader (McLachlan et al., 2017). In doing this, antibodies surround a pathogen and take on three specific roles when confronting the invader: neutralization, opsonization, and complement activation. In neutralization, antibodies completely cover the pathogen, taking away the ability for it to infect any more cells. Opsonization occurs when the antibody-antigen complex alerts the immune system that something is wrong, and neutrophils and macrophages come around to ingest and destroy the pathogen. Lastly, complement activation is a way to directly destroy bacteria (“Immune Cells,” 2014). We also have a certain subset of B cells called memory B cells. These have the ability to recognize and respond to the same antigen in the future, initiating a faster response than the initial exposure (Banasik & Copstead, 2019). Memory B cells also have a major role in how vaccines work (Palm & Henry, 2019).

In giving a full picture of the immune system, we also highlight neutrophils, eosinophils, basophils + mast cells, and NK cells. Neutrophils make up 60-80% of our WBC count and are potent defenders against bacterial infections. They respond in large numbers very quickly, engulfing and destroying microorganisms. Eosinophils are big players in neutralizing parasitic infections. Basophils and mast cells initiate the inflammatory response that we see in allergic reactions. Lastly, natural killer (NK) cells target and kill tumor cells and cells infected with viruses without any prior exposure, unlike the T and B cells described before (Banasik & Copstead, 2019).

The immune system is complex and extensive, and it defends our body all day and every day. With all of this in mind, the next time you’re feeling sick and your lymph nodes feel swollen, remember to rest up to give all of these powerful cells the chance to keep you healthy!

Reference List

Banasik, J. L., & Copstead, L. E. (2019). Pathophysiology. Elsevier. 

“How the Immune System Protects You From Infection | Pfizer.” Accessed March 1, 2022. https://www.pfizer.com/news/articles/how_the_immune_system_protects_you_from_infection.

“Immune Cells | NIH: National Institute of Allergy and Infectious Diseases.” Accessed March 1, 2022. https://www.niaid.nih.gov/research/immune-cells.

McLachlan, J. B., Hart, J. P., Shelburne, C. P., Staats, H. F., & Gunn, M. D. (2017). Understanding how lymph nodes respond to infection may redefine how immune system functions. Duke Health. Retrieved March 2, 2022, from https://corporate.dukehealth.org/news/understanding-how-lymph-nodes-respond-infection-may-redefine-how-immune-system-functions