Psoriasis is almost always a chronic skin disease which may also affect the joints. With a frequency of 1 to 3 percent in western industrial nations, psoriasis is one of the most common dermatological diseases. Almost 1.6 million people are affected in Germany alone. Psoriasis can occur at any age, but it appears particularly frequently in people 15 to 25 and 50 to 60 years of age.

Psoriasis cannot be cured to date. In nine out of ten cases, the inflammatory processes advance chronically, whereby the centers slowly increase in size. In less severe cases, psoriasis represents more of a cosmetic problem, but it can greatly limit the patient's quality of life in more severe cases.
 
Psoriasis is an autoimmune disease. This means that the human defense mechanism (immune system), which protects against pathogens, can no longer distinguish between foreign components and the body's own components and itself causes a disease.
 
What causes the immune system's erroneous programming and why the defense mechanism can no longer distinguish between "self" and "foreign" is not yet known in detail. The human organism – even a healthy one - repeatedly creates immune cells, which turn against the body's own tissue. These "autoreactive" T cells are however immediately recognized and incapacitated by the intact immune system before they can do any damage. Specialized immune cells, so-called regulatory T cells (Tregs) are responsible for this. Through direct contact with the cells they inhibit the autoreactive T cells and thus impede their attack on the body's own tissue.
 
This is different in patients with psoriasis: in this case the Tregs are not fully functional for some as-yet-unknown reason and their number among the total number of immune cells is decreased. The autoreactive T cells are therefore not sufficiently suppressed. They can multiply to a large extent unhindered and attack skin structures. One modern therapeutic strategy for autoimmune diseases as pursued by Biotest is therefore targeted toward re-establishing the Tregs' functionality so that they are able to reassume their natural control function against autoreactive T cells (Biotherapeutic agent BT-061)