Immune Cartoon

Pandemics can reveal a lot about your life. How comfortable is your couch after sitting for 30 consecutive days? Can you stream every show ever mentioned by your friends? Does your job really require pants?

For me, the pandemic also revealed how much I needed to learn about the immune system. As I dove into the research, I was blown away.

The immune system is an incredible saga. Battles rage in our bodies on a daily basis. These battles may escalate into wars. When the wars end, our immune system forgives but never forgets. We keep the best-trained soldiers in the field in case the enemy returns. Sometimes, the wars spiral out of control and refuse to end.

Learning about the immune system is like watching Game of Thrones. The immune system’s different cells and pathways come alive as a war story.

We live in a cloud of cellular threats. Our body does an amazing job navigating and fighting the attacks. With a basic understanding of the immune system, we can help our immune system perform. We can make smarter choices with our diet and lifestyle.

So to help people get started learning about the immune system, I illustrated the war story from my imagination. I call it the immune cartoon.

Immune System 101

Our immune system uses two response systems to protect our health. Our innate system attacks an infection where it occurs. I like to think of the innate system as little battlefields.

The other system is the adaptive, or specific, system. This response kicks in when our innate system is overwhelmed. In other words, when our body is losing the battle, we send out signals to start a war. There is also a complement system that works between the two, but we won’t get into that today.

Innate System

Macrophages are a type leukocytes (white blood cells) that recognize and attacks the enemy cells.

The next battle could break out at any minute. Cellular soldiers – called macrophages – patrol tissues in our body. These cells are on the front lines. They keep watch for suspicious enemy cells, and when they recognize a germ sneaking around, macrophages are the first to attack.

A pathogen is a disease causing organism like a virus or infectious bacteria.

Our bodies are built with physical and chemical barriers to protect against cellular enemies, a.k.a pathogens.

We are initially protected by physical barriers including the mucosa of respiratory, gastrointestinal and urinary tract.

From time to time, these barriers will fail us. We might get a cut, or maybe the enemy sneaks through a gap in the fence. Macrophages cruise around using their receptors to scan for invasions.

Macrophages contain a variety of receptors – including toll-like receptors – to recognize PAMPS.

When an enemy is recognized, the macrophages jump into action. The innate immune system is activated.

The battle is on. Macrophages – and other phagocytes like neutrophils – use a gnarly process called phagocytosis to basically eat up the enemy.

The macrophage wraps the outside of its cell (membrane) around the pathogen – engulfing the pathogen in a little bubble (phagosome). We are talking a PAC-man style attack. Once the pathogen is completely absorbed inside the macrophage, surrounding enzymes (lysosome) fill the bubble and break it down into harmless digestible parts.

Phagocytosis is the process of absorbing a particle, internalizing (phagosome) and destroying it with digestive enzymes.

Chomp. Chomp. Just like that, the battle is over. The macrophage wins. The innate immune system worked.

But what happens if our cellular soldiers on the front lines can’t keep up with the enemy attack?

The battle escalates into a war.

Macrophages can trigger inflammation when they are overwhelmed.

Macrophages can call for back up by releasing cellular messenger pigeons called cytokines. When cytokines are released, the process of inflammation starts.

Cytokines are proteins that trigger processes and recruit macrophages, monocytes (macrophage precursor) and neutrophils.

The first phase of the war is called the acute phase response. This is when inflammation stimulates the release of a special group of cytokines called interleukins. Different types of interleukins travel across the body.

Interleukin 1 (IL-1) goes to the brain. IL-1 says to the brain, “we got a situation here. Let’s turn up the heat and see if the enemy melts on the battlefield.” The body starts a fever. “But also, we’re going to need to use more energy in this war. Conserve some energy for us,” says IL-1. The body becomes tired and loses appetite.

Opsonins are acute phase proteins produced in the liver that help macrophages snatch up pathogens.

Interleukin 6 (IL-6) travels to the liver for an important mission. IL-6 tells the liver to start producing weapons for the macrophages. Our cellular soldiers can use these weapons (opsonins) to latch onto pathogens and suck them into their cells (phagocytosis). The liver brings weapons to the battlefield, and macrophages use these tools to swoop up the enemy.

Other types of interleukins are released to recruit a variety of different types of soldiers to the battlefield.

Adaptive System

The war starts when the messenger pigeons fly around sending signals and recruiting help. The adaptive system is activated. The immune system is ready to bring in the heavy artillery.

T cells and B cells are lymphocytes floating around the lymphatic system and blood.

T cells and B cells are the big guns. These cells are waiting in our lymph nodes and lymphatic tissue. Each cell is trained to fight a specific pathogen. There are millions of different T cells and B cells trained for different fights.

These cells need a peek at the enemy to know if it’s the enemy they are trained to fight. The immune system uses an amazing process to give the T cells a glimpse of what they’ll face on the battlefield.

A special messenger cell called a dendritic cell is sent to the battlefield. This cell will study the enemy – paying close attention to the most unique characteristics of the enemy (antigens).

Antigens are the molecular structures of pathogens. T cells receptors identify antigens. B cells have antibodies for antigens.

Then the dendritic cell changes into a costume. The cell dresses up in the enemy’s uniform…

The dendritic cell displays the antigens on its cell surface.

…and parades into the barracks for the T and B cells to check out.

Then the dendritic cell travels into the lymphatic tissue where it presents antigens on the HLA Class II molecules to T cells.

When T cells recognize the enemy they were trained to fight, they activate and prepare for battle. Activated T cells spawn a special forces team of helper cells and send messenger pigeons to recruit the right B cell with the right antibodies.

T cells proliferate with T helper cells and product cytokines. B cells proliferate with plasma cells and memory b cells.

The B cells will spawn their own special forces team. This team will consist of plasma cells to produce additional antibodies as well as memory cells. The memory cells will hang around after the war is over so that they can jump back into battle if the enemy ever returns.

Plasma cells produce antibodies specific to the antigen. Antibodies destroy the pathogen a few different ways.

To be continued…

What happens next? How does the war end? Subscribe here to receive an alert when part II is published.