Idiopathic inflammatory myopathies (IIMs) comprise a heterogenic group of inflammatory musculoskeletal diseases (IMDs) in which interactions of infiltrating immune cells with local cells in the muscle, lead to the progressive, autoimmune-mediated destruction of muscle tissue. The detailed pathophysiology is insufficiently understood and the therapeutic options are limited. However, there are several subtypes of IIMs that are characterized by specific patterns of affected muscle groups and extramuscular organ involvement including the skin, lung, and joints. The local mesenchymal environment in the muscle as consisting of skeletal muscle cells, endothelial cells and fibroblasts appears to be critical for IIM development and progression. Therefore, a dysfunction of the underlying regulatory mechanisms might be fundamental to the pathogenesis and disease pattern of IIMs. However, the exact mesenchymal signature of the inflamed muscle tissue and non-cellular signatures such as cytokines, chemokines and extracellular vesicles (EVs) as secreted by mesenchymal cells as well as their influence on peripheral blood immune cell composition is largely unknown. Therefore, we intend to investigate these signatures in different IIMs and compare them to those signatures found in other organ specific IMDs. To this end, blood and tissue will be collected from IIM subtypes (dermatomyositis - DM, sporadic inclusion body myositis – sIBM and antisynthetase syndrome - ASS) and other IMDs in frame of our established National Myositis Network and the consortium. The biomaterials will be used for an unbiased analysis of cellular parameters as well as non-cellular signatures. The establishment of such signatures will help (i) the diagnosis of different IIM subtypes, (ii) to predict organ involvement in myositis at early disease stages and (iii) identify novel therapeutic concepts to be transferred to IIMs.