How does the immune system work?

El sistema inmunitario es el sistema de defensa natural del organismo. No reside en una sola parte del cuerpo; es más bien una red de células, moléculas, tejidos y órganos que, en conjunto, lo

The immune system is the body’s natural defense system. It does not reside in one single part of the body—rather, it is made up of a network of cells, molecules, tissues, and organs working together to protect the body. Each of these elements plays a key role in how the immune system works and its function as a whole, which is crucial to preventing infection or disease, including cancer.

The body’s powerful immune system can protect us against cancer, and is capable of eliminating tumors that have formed. Immunotherapy is a class of treatments that taps into the immune system’s power. By doing so, immunotherapy can enable the immune system to target and potentially cure all types of cancer, ultimately saving more lives.

There are two branches of the immune system, the innate immune system and the adaptive immune system. The innate immune system provides a general defense against common pathogens (any bacteria, virus, or other disease-causing microorganism), which is why it is also known as the nonspecific immune system. The adaptive immune system targets specific threats and learns how to launch precise responses against viruses or bacteria with which the body has already come into contact. The various components of the immune system work together to provide both types of protection.

THE CELLS OF THE IMMUNE SYSTEM

A number of different cells work together within the immune system to fight infections and disease. Each type of cell plays an important role in identifying, marking, and destroying harmful cells that enter or develop in the body.

B cells release antibodies to defend against harmful, invading cells. Each B cell is programmed to make one specific type of antibody—for instance, one B cell might be responsible for making antibodies that defend against the common cold virus. Tumor-reactive antibodies can bind to cancer cells, disrupting their activity as well as stimulating immune responses against them.

CD4⁺ helper T cells send “help” signals to other immune cells (such as the CD8⁺ killer T cells) to better direct their response and make sure that they destroy harmful cells as quickly and efficiently as possible. These cells also communicate with the B cells producing antibodies.

CD8⁺ killer T cells destroy thousands of virus-infected cells in the body every day. These cells can also directly target and destroy cancer cells.

Dendritic cells digest foreign or cancerous cells and present their proteins on their surfaces, where other immune cells can better recognize and then destroy the harmful cells.

Macrophages are known as the “big eaters” of the immune system. Macrophages engulf and destroy bacteria and other harmful cells. Like dendritic cells, they present antigens to other cells of the immune system for identification and detruction.

Regulatory T cells provide checks and balances to make sure that the immune system does not overreact. A chronic immune overreaction is known as an autoimmune disease.

THE MOLECULES OF THE IMMUNE SYSTEM

Antibodies are proteins that bind to specific markers known as antigens on harmful invaders, such as germs, viruses, or tumor cells. Antibodies also mark these harmful cells for attack and destruction, which is carried out by other immune system cells.

Cytokines are messenger molecules that help immune cells work together to coordinate the correct immune response to any given invader, infection, or tumor.

THE TISSUES AND ORGANS OF THE IMMUNE SYSTEM

How does the immune system work beyond the cellular and molecular levels? There is also an intricate system of tissues and organs that collaborate to protect the body from harmful cells and fight against disease, including cancer. These tissues and organs, including the appendix, bone marrow, lymph nodes, the skin, the spleen, and the thymus gland provide the broader framework in which the individual components of the immune system develop and operate.

The appendix is a thin tube located in the lower right abdomen. The exact function of the appendix within the immune system is unknown, and many people live without it—one theory is that the appendix acts as a storage site for “good” digestive bacteria (the microbiome).

Bone marrow is soft, sponge-like material found within the bone and a crucial part of the immune system. It contains immature cells that either divide to form stem cells (progenitor cells that can replenish other cell types as required), or mature into red blood cells (oxygen and carbon dioxide transport cells), white blood cells (which include B cells and T cells), and platelets (blood cells that form clots to stop bleeding).

Lymph nodes are small glands located throughout the body that filter out viruses, bacteria, and cancer cells, which are then destroyed by specialized white blood cells. The lymph nodes are also the site where T cells “learn” to destroy harmful invaders within the body.

The skin is the body’s largest organ and serves as a protective barrier that defends against pathogens and toxins. It also possesses its own immune cells and lymphatic vessels.

The spleen is an organ located to the left of the stomach that filters blood and provides storage for platelets and white blood cells. The spleen is also the site where key immune cells (like B cells) multiply in order to fight invasive, foreign cells.

The thymus gland is a small gland located in the upper chest, beneath the breastbone. It provides a place for key immune cells (like T cells) to mature into cells that can fight infection and cancer.

THE IMPORTANCE OF THE IMMUNE SYSTEM IN IMMUNOTHERAPY

Each element and process within the immune system is important to the body’s overall ability to protect against disease and harmful pathogens. The powerful coordination and communication of the immune system is such that it can be strengthened to fight off many types of cancer through treatments like immunotherapy. Learn more about why immunotherapy research matters and how the Cancer Research Institute’s innovative approach has shaped the progress of cancer treatments. You can contribute to continued breakthroughs in cancer research and treatment options by making a donation to the Cancer Research Institute today.