Meet the primary players of your immune system
“Now is the time to understand more, so that we may fear less.” — Marie Curie, physicist & chemist
These past few months, I’ve woken up at 4AM a few times in anxiety. So I started reading a human physiology book to fall back asleep. Inspired by what I read, I wanted to write this to help fill a gap between fear and understanding.
We know that our immune system plays a role in fighting off common colds and flus. Yet, who exactly are the primary players? Let’s look at how the immune system works, and get acquainted with the offensive and defensive teams.
How your immune system works
Your immune system defends the body from pathogens. Its network of cells, molecules, and tissues stretch across your body, from head to toe (Silverthorn, 2007). The primary players — white blood cells — each exhibit unique fighting traits. These players come together as a symphony to keep us healthy.
First, your immune system detects a pathogen, and signals in more immune cells to the infected area. Next, it coordinates its team to destroy the offensive, and keeps a memory of the visiting pathogen.
Here are a few important areas to keep in mind:
- primary lymphoid tissues: where immune cells form and mature (thymus gland & bone marrow)
- secondary lymphoid tissues: where immune cells interact with pathogens and start responding
- blood circulation: the highway used by immune cells to move around your body
Offensive Players
Pathogens, or organisms that cause disease, find your body to be a nice environment to grow in (NIH, 2003). Your immune system disagrees, and tries to eradicate these free-loaders. Like us, pathogens aim to survive and thrive. Antigens, found on pathogens and other molecules that drift into your body, are any chemical parts that trigger your immune system.
- bacteria: a single-celled organism that can reproduce on its own
- virus: DNA or RNA wrapped in a protein coat, that needs to hijack your body cell to reproduce
- parasite: a multicellular organism that lives off your body nutrients (think tapeworm)
- cancer cell: a regular body cell gone wrong with uncontrollable growth
- pollen: a powder from plants that some immune systems treat as a threat, causing allergies
Defensive Players
Origin
Every key player of the immune system originates from one place — your stem cells in the bone marrow (OpenStax, 2016). When you look at how each white blood cell develops, you’ll notice two distinct lineage lines. Those lines roughly lead to your two defensive teams: innate and adaptive.
Innate team
Your innate team isn’t specialized, but it’s quick. First to respond to an invading pathogen, the innate team launches a general and non-specific defense. Your innate team can recognize pathogens and abnormal body cells, but it can’t single out the different types.
Eaters: Neutrophils & Macrophages
Neutrophils, the most common type of immune cell, have an appetite for pathogens. They circulate in the blood and venture into your body tissues when they detect an infection (Silverthorn, 2007). Neutrophils swallow pathogens whole and digest them with lysosomes. Then they send signals to bring in more team members. Short-lived, neutrophils die within a few days.
Macrophages want to eat a buffet. Not only do they eat a truckload of pathogens, but they eat dead neutrophils, old red blood cells, and floating debris (NIH, 2003). Eating and chilling in your tissues, macrophages also send signals to your other players. Macrophages also show off the pathogens they’ve eaten to the adaptive team.
Destroyers: Natural Killer Cells
NK or natural killer cells, don’t care if you’re a fellow body cell. If you’re infected by a pathogen, they’ll detect and destroy you. NK cells scan the surface of body cells to check for normality. If they sense an infected or cancerous cell, NK cells release chemicals that cause cell death by apoptosis. Through destroying infected cells, NK cells help prevent the spread of viruses.
Presenters: Dendritic cells
Like macrophages, dendritic cells show off what they ate to the adaptive team. With extended projections, dendritic cells have a large surface area. Dendritic cells nibble on pathogens found in your skin and organ tissues. After, they glide over to secondary lymphoid tissues to meet with and activate adaptive players (Tanne & Bhardwaj, 2017).
Signalers: Basophils
Basophils circulate your blood, signaling to other immune cells for extra help. They hold large granules of chemical signals to release and enhance inflammation.
In an inflammatory response, you can feel and see swelling at the infected area of your body. This happens due to increased blood flow and congregating of immune cells.
Adaptive team
When your innate team passes the baton, the adaptive team roars in. A bit more sophisticated than innate, your adaptive team launches a targeted response to a specific pathogen. It takes your adaptive team a few days to create this specialized response. Adaptive players also act as historians, building up a memory of our previous battles.
Antibody Makers: B Cells & Plasma Cells
B cells create antibodies, or y-shaped proteins that latch onto specific pathogens. They then take their handmade goods and decorate the outer surface of their cells.
B cells can insert up to 100,000 antibodies into their cell membranes, increasing their reach for pathogens (Silverthorn, 2007). Activated from binding to a pathogen, B cells transform into memory B cells and plasma cells.
Plasma cells function more like antibody factories. Instead of decorating their cell membranes, plasma cells secrete a ton of antibodies.
Free-floating antibodies hit your blood circulation and head to infected areas. Plasma cells, larger than B cells, pack a big endoplasmic reticulum, the machinery that creates antibodies.
Tag, you’re ‘it’: antibodies
Antibodies help keep your blood circulation pristine by tagging and clumping pathogens. Tagging allows pathogens to be more visible to your immune system. Clumping brings pathogens together in one place, making them easier to deal with.
Your immune system saves these specific antibodies as memories. If the same pathogen shows up in your body again, those antibodies will latch on to them. Antibodies help eaters to eat, and cytotoxic cells to destroy.
Tale of two Ts: Cytotoxic T cells & Helper T cells
Cytotoxic T (Tc) cells are in the same league as NK destroyers; they also destroy infected cells by apoptosis. However, Tc cells can specifically recognize the pathogen presented on infected cells (Rosenberg & Huang, 2018). Equipped with a sensitive T cell receptor, Tc cells bind to destroy infected cells. They then create more Tc and memory T cells. Memory T cells quickly expand to fight when the same pathogen returns to your body.
On the other hand, helper T cells coordinate teamwork between the innate and adaptive (Alberts, 2002). They meet with immune cells that show off what they ate (macrophages, dendritic cells, and B cells). From taking a look at the presented pathogen, helper T cells become activated. Helper T cells then send encouraging signals that help B cells change into plasma cells. Their signals also help cytotoxic T cells destroy, and macrophages eat.
Conclusion
By taking a closer look at your immune system and its primary players, we can better understand the symptoms we see of the tiny wars waging inside. Our human biology can be fascinating, eye-opening, and not so intimidating to learn. At least, that’s what I’d tell my younger self.
“Science is beautiful when it makes simple explanations of phenomena or connections between different observations.” — Stephen Hawking, theoretical physicist
References
NIH. (2003). Understanding the Immune System.
OpenStax. (2016). The Lymphatic and Immune System. In Anatomy & Physiology.
Silverthorn, D. U. (2007). The Immune System. In Human Physiology: An Integrated Approach.
