Behcet's disease

Behcet disease, is a rare disorder and most of the symptoms are thought to be a result of an autoimmune process involving the blood vessels, so it’s a type of vasculitis.

Among the family of disorders that cause vasculitis, Behcet’s is fairly unique because it causes inflammation in blood vessels of all sizes—small, medium, and large ones—on both the arterial and venous side of the circulation.

The underlying cause of Behcet’s is unknown, but there are a number of clues.

The biggest clue is that the human leukocyte antigen, or HLA, genes seem to play a role, and this is based on the fact that having a specific type—the HLA-B51 type—predisposes individuals to having Behcet disease.

HLA genes encode proteins found on the surface of immune cells, and play a key role in regulation of those cells, and since the disease is a result of an autoimmune process, it makes sense that the HLA-B51 proteins could be involved.

Another, clue is that an individual’s response to viral and bacterial infections might be involved.

For example, some individuals with Behcet’s generate relatively high levels of antibodies to Helicobacter pylori which may go on to damage blood vessel walls.

And this is an example of molecular mimicry where an antibody to a foreign pathogen starts to cross-react and damage the person’s own tissue.

Individuals with Behcet’s also seem to have a weakened innate immune system, a higher proportion of autoreactive T cells, and activated neutrophils which destroy healthy tissue, as well as altered levels of T helper cells and cytokines.

In summary, these clues span genetic and environmental factors as well as both the innate and adaptive immune system.

When looking at the blood vessels in particular, the classic finding is seeing lymphocytes in the walls of capillaries, veins, and arteries of all sizes, making them inflamed and boggy.

Sometimes the inflammation can get so severe that the tissue around the vessel starts to die off completely.

These changes make the endothelial lining more likely to develop blood clots or aneurysms.

Since the inflammation is happening in blood vessels of all sizes throughout the body, people with Behcet’s can develop a wide-range of symptoms.