Animated Medical Graphics


Sarcoidosis is due to an abnormality in the way that the immune system functions. The immune system is very complex and serves to protect the body from germs and other foreign substances. It is made up of many different types of cells that perform different duties. Let's start with the basic structure of a cell, shown on the left. The cell is microscopic in size and is composed of a nucleus and cytoplasm. The nucleus contains DNA, which forms the genes, and tells the cell what to do. The cytoplasm contains the machinery of the cell and carries out the functions that the cell is responsible for.

Although the immune system contains a variety of cells, those that are involved in sarcoidosis are described below:

Helper T-Lymphocytes
Their job is to "tag" invading germs with special chemical substances so that the other cells of the immune system can easily recognize those germs and destroy them.
They eat germs that are tagged by the Helper T-Lymphocytes.
Giant Cells
They are formed by the fusion of many histiocytes. Their job is to eat germs or other substances that are too big to be eaten by individual histiocytes.
They lay down scar tissue to replace tissue that has been damaged. They also may produce scar tissue around the area where there are germs in order to stop the germs from spreading.

The problem in sarcoidosis is that there are no germs that we know of that cause this disease. For some unknown reason, there seems to be a false alarm that causes the Helper T-Lymphocytes to congregate and secrete the "tagging" chemicals that attract the other cells of the immune system. This sequence of events is demonstrated on the left. The entire cluster of cells is somewhat smaller than a grain of sand and is called a granuloma. This type of reaction is referred to as granulomatous inflammation. Many of these granulomas are formed in sarcoidosis. Usually, the immune system eventually recognizes its error and the process subsides. But it may progress to the point where the fibroblasts produce excessive amounts of scar tissue. It then becomes very difficult to reverse the condition with treatment.

In the U.S. sarcoidosis occurs more often in people of black African descent than in other races, and is rare in Chinese and southeast Asians. It often affects the lungs, chest lymph nodes, eyes, and skin. In the lungs the granulomatous inflammation may interfere with breathing and therefore can produce shortness of breath. X-rays may show abnormalities in the chest. A laboratory blood test that is frequently done when sarcoidosis is suspected is the ACE (angiotensin converting enzyme) level, which is usually elevated in sarcoidosis. A lung biopsy may also be done to look for granulomas.

Note: The material provided in this web page is educational in nature and not medical advice. It is meant neither for self-diagnosis nor as a treatment recommendation. If you are concerned about any condition you think you may have, CONSULT YOUR DOCTOR.