New understanding of how treatment with dimethyl fumarate leads to improvements in psoriasis symptoms

Psoriasis is a chronic, inflammatory skin disease that affects approximately 2% of people. In the disease raised scaly plaques are found on the skin and this is driven by problems with the immune system. There are various treatments for psoriasis from topical (applied to the skin) creams and phototherapy (a type of light treatment) for mild psoriasis, to oral (taken by mouth) and injectable drugs for moderate‐to‐severe disease. One of the oral treatments that has been widely used in Europe for psoriasis is dimethyl fumarate (DMF, marketed as Skilarence™). Although DMF has been in use for many years, the mechanism by which it works to improve symptoms in patients with psoriasis is unclear. In this study we examined the effects of DMF on T cells, which are key immune cells involved in psoriasis. We found that DMF treatment in patients with psoriasis reduced the frequency of inflammatory T helper 17 (Th17) cells, which are known to contribute to the cause of psoriasis. On the other hand, DMF treatment increased levels of regulatory T (Treg) cells, which are anti‐inflammatory and protect against autoimmune disease (diseases, like psoriasis, where the immune system is involved). The overall result was that the ratio of Th17 to Treg cells, which is known to be out of balance in psoriasis, was corrected by DMF therapy. Furthermore, our study suggests that Treg cells were favoured over Th17 cells because of their enhanced ability to withstand the damaging effects that DMF exerts on cells. In summary, the improvements in psoriasis symptoms with DMF treatment may be explained by its selective reduction of harmful Th17 cells without a reduction in protective Treg cells. Linked Article :  Sulaimani et al. Br J Dermatol 2021; 184 :495–503.