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The Human Body and the Anatomy of the Immune System

The immune system consists of different parts of the human body that work together to identify and stamp out viruses, bacteria, and diseases. This body system encompasses the bone marrow, thymus, lymph nodes, spleen, and lymphoid tissue.

Bone Marrow

Bone marrow, a substance that's found inside of your bones, makes blood cells, including the white blood cells and platelets that your body uses to respond to illnesses and injuries. The pelvis contains the most bone marrow, but it's also found in the center of other bones.

Bone Marrow Donation: Why It's Needed and What to Expect: People with some serious diseases, like leukemia and sickle cell anemia, may need a bone marrow transplant, which requires other people to donate their bone marrow. The process of donating bone marrow involves having the cells removed while you're under anesthesia.
Bone Marrow Diseases: A variety of bone marrow diseases can have serious negative health effects.
What Is Bone Marrow? This page explains what bone marrow looks like and what it does.
What to Know Before a Bone Marrow Biopsy: If a doctor suspects that your bone marrow may not be working as it should, a biopsy might be necessary.
Bone Marrow Transplants: Some cancer patients need a bone marrow transplant because theirs is damaged during cancer treatments.

Thymus

The thymus is a gland that makes T cells, a specific type of white blood cell, and trains these cells to fight infections. It's located behind your sternum, between your lungs and just above your heart.

Thymus Gland: What it Is and How it Works: The thymus is a tiny gland that plays a big part in the body's response to infections.
Manipulating Immune Function and Thymus Recovery: Researchers have studied how to help the thymus recover faster after it's damaged by chemotherapy or radiation therapy.
The Lowly Thymus May Be Saving Your Life: A Harvard-led study found that the thymus plays a role in preventing cancer from developing.
The Role of the Thymus in Immune Reconstitution: A lot of the thymus's work is done before a person reaches adulthood, but it does continue to function decades later.
Thymus Gland Cancer: While it's rare to get cancer of the thymus, it is possible. Learn more about this condition here.

Lymph Nodes

Lymph nodes are responsible for filtering waste from your lymph fluid, including foreign matter like cancer cells, harmful bacteria, and invasive fungi like candida. Hundreds of lymph nodes are located all over the body, but they're most noticeable in your neck, armpits, and groin.

The Role of Lymph Nodes in Cancer Treatment: The lymph nodes will naturally try to filter out cancer cells, so people with cancer often have it in their lymph nodes.
Swollen Lymph Nodes: Infections can cause your lymph nodes to swell, up, a condition called lymphadenopathy. Once the infection is gone, the lymph nodes should return to their normal size.
Lymphadenopathy in Children: Swollen lymph nodes, sometimes called "swollen glands," are common in children because they can accompany common infections like strep throat or the flu.
Lymphadenectomy: If cancer is suspected in a lymph node, it may need to be surgically removed and examined.
Lymphedema: Lymphedema is swelling that's caused by a buildup of lymphatic fluid.

Spleen

The spleen is an organ that filters and stores blood. It's made of red pulp, which removes damaged blood cells, and white pulp, which makes white blood cells.

What Does the Spleen Do? Inside the spleen, damaged blood cells are filtered out and broken down.
Splenic Sequestration Crisis: When someone has sickle cell anemia, these malformed cells can clog up the spleen, trapping blood inside and causing the spleen to enlarge.
How the Spleen Filters Blood: Research has found that a slit inside the spleen acts as a filter that keeps misshapen blood cells from passing through.
Splenic Conditions: If you have an infected or ruptured spleen, prompt medical treatment is essential.
Enlarged Spleen (Splenomegaly): Many conditions can cause an enlarged spleen, from a viral infection to cancer or lupus.

Mucosa-Associated Lymphoid Tissue (MALT)

Mucosa-associated lymphoid tissue, or MALT, is located throughout the body in the mucosal linings of organs and body cavities. Mucosal tissues are good places for pathogens to enter the body, and when this happens, MALT begins the body's immune response.

MALT: Musoca-Associated Lympatic Tissue: This brief video outlines where MALT is found in the body.
A Case Study of Lymphoid Tissue Lymphoma: Doctors in Hong Kong examine the case of a man with cancer of the lymphoid tissue in this study.
Mucosal Surfaces and Immune Tolerance: Learn more about how MALT works with this chapter from an educational text.
Structure, Function, and Histology of Mucosa-Associated Lymphoid Tissue: This scientific paper examines the specifics of how MALT works and how these tissues change over time.

Lymphocyte Recirculation

Lymphocytes are the white blood cells that help your body to fight infection, and they travel throughout the body between the lymphatic and circulatory systems in a process called lymphocyte recirculation.

Lymphocyte Migration and Inflammation: These slides illustrate how lymphocytes travel through the body and capture antigens.
Mathematical Modeling Reveals Kinetics of Lymphocyte Recirculation in the Whole Organism: Take an in-depth look at the process of lymphocyte recirculation by reading this academic paper.
Lymphocyte Trafficking in the Intestine and Liver: This journal article examines how lymphocytes constantly monitor the body for infection and how they react when they find it in the gut.