A doctor discusses the immune system

What is the Immune System?

Your immune system is responsible for helping to eliminate invaders and infectious organisms from your body before they are able to harm you. This can include bacteria, microbes, viruses, toxins, and parasites—all of which could have the power to kill you if it weren’t for your immune system.

What makes up the immune system?

Your immune system is a very complex collection of structures and processes that work inside your body. The main components of the immune system include:

  • Lymph nodes: These organs are small, bean-shaped structures that store cells that help to fight infection and disease. Lymph nodes also contain lymph, which is a clear fluid that is able to carry the infection-fighting cells to different parts of your body whenever necessary. When your body is fighting an infection, this is why your lymph nodes become enlarged and may feel sore.

  • Spleen: This is the largest lymphatic organ in your body, located on your left side under the ribs and above the stomach. Your spleen contains white blood cells that work to fight infection and disease. It also helps to control the amount of blood in your body and disposes of old or damaged blood cells.

  • Bone marrow: This is the yellow, spongy tissue that is located in the center of your bones that also produces white blood cells. Some of the most important cells in your immune system originate in your bone marrow.

  • Lymphocytes: These are small white blood cells that play a huge role in defending your body against disease. There are two types, called B-cells and T-cells. B-cells make antibodies that attack bacteria and toxins while T-cells help to destroy infected or cancerous cells.

  • Thymus: This is a small organ shaped like a thyme leaf and located beneath the breastbone while T-cells mature.

  • Leukocytes: These are the disease-fighting white blood cells that identify and eliminate pathogens in the body. When you have a high white blood cell count, this is referred to as leukocytosis, and it means that your body is fighting off an infection.

How does the immune system protect you?

When a virus or bacteria invade your body and begins to reproduce, this normally leads to symptoms of a sickness. For example, the bacteria that causes strep throat releases a toxin that causes inflammation in your throat. Your immune system’s job is to protect you from these infections. It does this in a number of ways, including:

  • Creating a barrier that will prevent bacteria and viruses from entering your body. Tears, mucus, and saliva are all covered in an enzyme called lysozyme that breaks down the walls of bacteria or viruses that it comes into contact with. 

  • Detecting and eliminating viruses and bacteria that do happen to get inside your body before they are able to start reproducing. 

  • If the virus or bacteria is able to start reproducing and causing problems in your body, your immune system is responsible for fighting it off and taking care of it

Last Updated: November 23, 2015