Relevance of the stroma and epithelial-mesenchymal transition (EMT) for the rheumatic diseases

Epithelial-mesenchymal transition (EMT) is a term applied to the process whereby cells undergo a switch from an epithelial phenotype with tight junctions, lateral, apical, and basal membranes, and lack of mobility into mesenchymal cells that have loose interactions with other cells, are non-polarized, motile and produce an extracellular matrix. The importance of this process was initially recognized from a very early step in embryology, but more recently as a potential mechanism for the progression and spread of epithelial cancers. As the sequence of morphological changes has become understood in molecular terms, diseases characterized by alterations in stromal elements and fibrosis are being considered as examples of EMT. This review will focus on the pathogenetic features of immune-mediated renal disease, systemic sclerosis and rheumatoid arthritis that could be explained by EMT.