Sarcoidosis and possible causes
Sarcoidosis may or may not be an autoimmune disease
No one knows exactly what causes sarcoidosis, although our understanding of how it develops continues to improve. Experts currently believe that one or more exposures in people with a particular genetic background may trigger cellular reactions and the recruitment of inflammatory cells into affected organs—in other words, something activates the immune response. Some studies suggest that bacteria, viruses or chemicals may trigger the disease. Although these triggers are usually harmless to most people, they may irritate the immune system in people who have a genetic risk of developing sarcoidosis.
There are theories that the immune response may be overactive or, in some cases, inappropriate, resulting in persistent inflammation, granuloma formation and, in some cases, scarring or fibrosis. There is growing evidence that this immune response in sarcoidosis may also include an “autoimmune” response, with reactions against some “self” proteins. However, at present we do NOT consider sarcoidosis to be predominantly an autoimmune disease like rheumatoid arthritis (RA) or systemic lupus erythematosus (lupus).
Although the role of autoimmune mechanisms is not yet well understood, some studies have found antibodies against human proteins at increased rates in some patients with sarcoidosis compared with people with and without sarcoidosis. In addition, cells from some people with sarcoidosis show an immune response to some of the body’s own proteins, resembling autoimmune disease.
The precise role of this “autoimmunity” in sarcoidosis is unclear, although it is being actively studied. It is not clear whether the reaction to self-proteins is the main cause of granulomatous inflammation or whether it is merely a bystander caught up in a larger reaction.
The presence of this “autoimmune” process could support the use of some treatments tested in patients with sarcoidosis, such as rituximab. At present, although we do not consider sarcoidosis to be the same as diseases such as RA or lupus, studies show that some immune reactions and genetic factors are shared between these conditions. Some autoimmune diseases also occur together with sarcoidosis more often than would be expected by chance, including Sjögren’s disease and others, raising the question of whether they share some mechanisms. By better defining the mechanisms that cause sarcoidosis—including the roles of inflammation, excessive or insufficient immune responses and autoimmunity—we may be able to treat patients more effectively and perhaps one day prevent the disease.
In short, although there are some similarities, based on current science we do not recommend using the label “autoimmune” to describe sarcoidosis.
What are the risk factors?
Once thought to be rare, sarcoidosis is now known to be common and to affect people worldwide. It can affect people of any age, race or sex. However, it is most common among adults between 20 and 40 years of age and in certain ethnic groups. Disease severity may vary according to race or ethnic background.
In the United States, sarcoidosis is most common among African Americans and people of European—particularly Scandinavian—ancestry. These groups may also experience more severe and chronic forms.
Among African Americans, the most affected group in the United States, the estimated lifetime risk of developing sarcoidosis may be as high as 2 percent.
The disease is slightly more common in women than in men.
The disease manifests differently in different groups. Although the lungs and lymph nodes are affected in almost everyone with sarcoidosis, African Americans and people of Japanese ancestry are more likely than white people to have eye involvement. Skin nodules are more common among people of northern European ancestry, while people of Japanese ancestry appear to be more prone to sarcoidosis-related heart problems.
Research also suggests that the risk may be increased to some extent if someone in a person’s close family has sarcoidosis, although researchers have not yet identified the gene or genes associated with its development.
Source: https://www.stopsarcoidosis.org/what-is-sarcoidosis/causes-risk-factors/