• Reviewed on 8/12
    By Dr. Abbott

Immune Deficiency: Overview

In general, an immune deficiency is a disease of the immune system. The immune system protects the body from infection. With an immune deficiency, the immune system is unable to protect the body from infection as well as it should. This can lead to frequent or unusual infections that people with normal immune systems do not get.

In most cases, an immune deficiency is a genetic problem.  This means that it is present at the time of birth and persists throughout life. Each immune deficiency is different. The genes involved in the immune deficiency determine the types of infection that you need to worry about getting. You and your doctor can work together to prevent the infections that your immune system has trouble preventing.

How the Immune System Works

The immune system normally protects your health in two very important ways. First, it recognizes “foreign invaders” like bacteria, viruses, parasites and fungi. Once the invaders are recognized, the immune system reacts by sending special cells and proteins to eliminate the infection. This is called the immune response.

The immune system isn’t located in just one part of the body. The thymus, liver, bone marrow, tonsils, lymph nodes, spleen and blood all have a role in the immune response. These organs help make, store and transport the cells and proteins that fight foreign invaders.  

The major cells and proteins of the immune system are:

  • B-cells (also called B-lymphocytes)
  • T-cells (also called T-lymphocytes)
  • Phagocytes - “Eater Cells”
  • Antibodies – Special proteins in the blood
  • Complement – Another type of proteins in blood



B-cells make antibodies, also called immunoglobulins or gammaglobulins. Antibodies are sent through the blood to all parts of the body in order to fight infection. 


T-cells travel in the blood to infected areas. Helper T-cells tell the immune system when more help is needed. Killer T-cells attack foreign invaders like infectious organisms.  Regulatory T-cells tell the immune system that something should be ignored, as is the case for your own body parts.


Phagocytes are in the blood and tissues. They eat and kill foreign invaders. Phagocytes send chemical signals to other phagocytes and help make complement. When antibodies and/or complement have coated the foreign invaders, it is easier for phagocytes to eat them.


Antibodies surround and coat the cells of foreign invaders.  This weakens the invader cells.  Some examples of antibodies are IgM, IgG and IgA. IgM antibodies travel to the site of infection when it first begins. IgG antibodies are found in the blood and tissues. IgA antibodies are in secretions like tears, saliva, mucus, and gastric juices. Antibodies are made by B cells.


Complement is made up of 18 proteins in the blood. The presence of foreign invaders and antibodies tells complement to start its work. Like antibodies, complement coats foreign invaders so that they are easier for phagocytes to eat and kill. Complement also sends signals to phagocytes when more are needed.

B-cells, T-cells, phagocytes, antibodies, and complement all work together to protect us. That’s what makes the immune system a system.

More Immune Deficiency Disorder Information
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