Understanding the Immune System: A Guide for Beginners

Elizabeth Marglin

by | Updated: October 22nd, 2018 | Read time: 5 minutes

Think of our immune system as our own private guardian of our galaxy, protecting us from invaders, germs, and killer cells.

We all talk about immunity, but no one really knows how exactly the immune system works. We have vague notions, at best, of how the immune system tries to protect us from getting sick. So how do we begin to get a grasp on how this vast network of cells, tissues and organs that work synergistically to keep us healthy? This guide is here to help.

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What is the immune system?

The immune system defends against infectious organisms and other invaders. Through a process called the immune response, the immune system attacks substances that invade body systems and cause disease. It’s a multi-pronged mechanism with a handful of primary players, listed below.

The primary components of the immune system:

The tonsils and the thymus: These produce antibodies that attack foreign invaders. 

Lymphatic system: This network, made of lymph nodes and vessels, carry lymph fluid, nutrients and waste material into the bloodstream. As it disperses fluid it also filters it, trapping bacteria, viruses and other invaders. Special white blood cells called lymphocytes are deployed to destroy the invaders.

Bone marrow: Soft tissue found inside the long bones of the arms, legs, vertebrae and the pelvic bones produce red and white blood cells along with platelets and yellow marrow. Yellow marrow helps produce some of the white blood cells necessary for healthy immunity.

Spleen: The spleen filters the blood through excreting old or damaged cells or platelets. It also pitches in on the bacteria-destroying mission of the lymph. 

White blood cells: Created by bone marrow, these cells protect your body from infection. If an infection develops, it’s the white blood cells that rush to the rescue, attacking the bacteria, allergen or virus.

What happens during an immune response?

A growing body of evidence suggests that our immune response to cancer is similar to its response to allergens—the body identifies both as threats of similar magnitude, although the allergic response is an overreaction.

Allergies, however, serve as a good example of how the immune response works. During an allergic reaction, an overly vigilant immune system orchestrates a complex mix of cellular and chemical interactions within the body. (The most common outcome is the lovely twofer—congestion and postnasal drip.) First, the immune system’s scouts, called antigen presenting cells (APC), surround the allergen. These cells divvy up the allergen into smaller fragments, which then combine with special proteins in the cell, called human leukocyte antigens (HLA). This dynamic combo, the allergen and the HLA, make these cells standout and command the attention of lymphocytes (white blood cells), who recognize them as foreign.

Lymphocytes are key players in immunity. They are divided into two main types, the T (mature in a gland in chest area) and B lymphocytes (mature in the bone marrow). The T-lymphocytes have a range of functions: attacking foreign substances (killer), assisting the immune response (helper), and creating an army of antibodies to bind to the allergens. The T-lymphocytes’ helpers are the B-lymphocytes, tiny antibody factories that spring into action on demand

Each T lymphocyte, or T cell, is a micro detective whose mission is to identify the invader. If the allergen is recognized as foe, it triggers an army of helper T cells that release chemicals (cytokines) to stimulate B lymphocytes. Now B lymphocytes produce the IgE antibodies even though they remain on standby. In a process called priming, the IgE attaches to the mast cells and basophils, unstable cells prone to explosive behavior. When the IgE binds to these volatile cells, they become like ticking time bombs.

Once primed, mast cells and basophils can remain ready to ignite with IgE for months or even years. A small number of B and T cells persist in the blood with the memory of the allergen, allowing them to activate and destroy viruses more quickly next time they enter the body.

Now the IgE is ready to bind to the invader. Included in their arsenal are mast cells, which have granules of histamines.

Degranulation–when the granules burst and the chemicals release like a small explosion–is the crux of the immune response. These histamines produce the common allergic symptoms. Typically, there is an immediate response (such as a runny nose), which sometimes progresses into a late phase response (more inflammation). Whether your immune system if fighting an allergy, a sickness or a cancer, the immune response is similar. The symptoms you experience with colds or allergies are not only the result of the virus, they are also the result of your body’s immune response to the invading party.

Types of immunity

Ever wonder why some people get sick all the time and others not so much? There are three types of immunity—innate, adaptive and passive.

Innate immunity

Everyone is born with some natural immunity that serves as a general protection. For example, many of the viruses that cause disease in other species don’t affect us at all. And animals are born with natural immunity that protects them from susceptibility to human diseases.

Innate immunity also includes the body’s external lines of defense, like the skin and mucous membranes that prevent disease from entering the body.

Adaptive immunity

Adaptive immunity develops throughout our lives and is the sum of our exposures to disease as well as our vaccinations against diseases.

Passive immunity

Passive immunity is a short-term or borrowed immunity from a person, typically a child’s mother. For example, maternal antibodies are transferred to a baby through the placenta. It can also be induced artificially through injections that contain targeted antibodies.

What are the most common immune system disorders?

If your immune system is significantly compromised, you might end up with a weakened immune system that can progress into a full-blown disorder. Here are the most common.

  • immunodeficiency disorders (either genetic or acquired)
  • autoimmune disorders (in which the body’s own immune system attacks its own tissue as foreign matter)
  • allergies (in which the immune system overreacts in response to an antigen)
  • cancers of the immune system, such as leukemia and lymphoma

Although you can’t prevent an immune system disorder, you can do your best to strengthen your immune system and give your body a fighting chance against the disease.