Juvenile dermatomyositis (JDM) is a rare systemic autoimmune disease characterized by muscle weakness and a distinctive skin rash. Many physicians treating dermatomyositis (DM) focus on the weakness and the resulting physical dysfunction as the most disabling features. The skin disease is often regarded as a less severe manifestation of illness; therefore, its therapy is not prioritized. Because the skin disease of DM can be as debilitating as the muscle disease, and because it significantly impacts the outcome of this illness, rapid and effective therapy must be identified.
Most of the previous studies of JDM concentrated on cells, including dendritic cells, of the immune system that recognize and respond to invaders, such as microbes. Mast cells, a pivotal component in the allergy system, had not been considered. The laboratory of Lauren Pachman and colleagues investigated the distribution of both mast cells and dendritic cell subsets.Paired muscle and skin that either had the inflammatory rash of JDM, or skin that appeared to be normal from untreated children with JDM were analyzed. Inflamed as well as normal appearing JDM skin contained many more mast cells than skin from pediatric controls, but no difference was seen in number of mast cells in muscle. Both JDM muscle and skin showed more mature plasmacytoid dendritic cells (pDCs), which play a critical role in the induction of autoimmune disease and other skin diseases. This identification of mast cells in JDM skin indicates that they have a specific function in JDM skin pathophysiology and that they appear to work with the pDCs to initiate the inflammatory cascade. The authors believe that a further understanding of these pathways will shed light on the often drug-resistant cutaneous inflammation and disease state, leading to more effective treatments.
The first author of the study, to be published in an upcoming issue of Arthritis and Rheumatism is Sheela Shrestha, MS. The article is also the subject of an editorial in the issue, whose authors commented: “Shrestha and colleagues describe several novel findings related to the pathogenesis of the skin disease of patients with juvenile DM, and extend observations on the type I interferon pathway, in a carefully conducted study that not only controls for disease state and treatment, but also pairs skin and muscle tissue in simultaneous examinations.”
Lauren Pachman, MD, is a professor of pediatrics at the Feinberg School; attending physician in the Division of Rheumatology at Children's Memorial; director of the Chicago City-wide FOCIS Center of Excellence in Clinical Immunology; and director of the Cure JM Program of Excellence in Myositis Research of the research center.
For more information contact Peggy Jones at 773.755.6341.
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