Causes of Sarcoidosis
The cause of sarcoidosis is unknown. Because the lungs and thoracic lymph nodes (the lymph nodes located in the chest) are the most frequently involved organs, some physicians and researchers suspect that sarcoidosis may be caused by something that enters the body through the lungs, that is, something that is inhaled such as a virus or bacteria, or an unidentified environmental toxin.
In particular, there is some evidence that sarcoidosis may be associated with Mycobacterium tuberculosis, the bacterium that causes tuberculosis. Sometimes sarcoidosis and tuberculosis occur simultaneously, suggesting they may have the same cause. Also, scientists have found M. tuberculosis DNA in infected sarcoidosis tissue, suggesting the bacteria is present and may be causing the disease. On the other hand, it may be that a patient with sarcoidosis has a suppressed immune system, making them more susceptible to tuberculosis. Or, a patient with TB may be more susceptible to sarcoidosis. One may not have anything to do with the other except that if you have one, your body is defenseless against the other. Sarcoidosis also resembles berryliosis, a disease caused by inhalation of the metal berrylium.
There is some evidence of geographical clustering, meaning the disease tends to occur with greater frequency in certain geographical areas. This suggests an environmental cause (i.e., if everyone in the area is breathing the same environmental toxin, and if sarcoidosis is caused by that toxin, people living in the area where the toxicity is high are more likely to develop the disease) or transmissible agent (i.e., if one person in the area has sarcoidosis, and it is infectious, other people in the area are likely to get infected).
No matter whether the trigger is a chemical toxin or bacteria, sarcoidosis involves a malfunctioning immune system. It is not really clear what the problem is and how it begins. It may even have a partial genetic basis.
It is not clear whether there is a link between characteristics of sarcoidosis and certain HLA (human lymphocyte antigens) patterns or not. HLAs are a type of histocompatibility antigens (proteins on the surface of the cells that serve as an important part of the body's defense against foreign invaders, such as viruses and bacteria). There are many different types of HLAs and many different forms of each type of HLA.
Familial sarcoidosis occasionally occurs, suggesting that there may be an inherited genetic component.