Pathogenic helper T cells.

Intractable chronic inflammatory diseases, including autoimmune diseases, autoinflammatory diseases and allergic diseases, are caused by disruption or failure of the immune system. Pathogenic immune cells are presumed to be closely related to the pathogenesis of intractable diseases, but the precise cellular and molecular mechanisms underlying the pathogenesis of these diseases remain unclear. The balance between the T helper type 1 (Th1) and Th2 cell fractions has been believed to be responsible for the differences among inflammatory diseases. However, an analysis of the cells infiltrating inflammatory lesions in mice and humans revealed the generation of pathogenic Th cells with different characteristics at the memory T-cell stage in the peripheral tissues in various inflammatory diseases. In this review, we will summarize and discuss recent progress regarding the characteristics of pathogenic Th cells, their mode of action, and the molecular mechanisms that regulate the pathology of intractable chronic inflammatory diseases, particularly those with tissue fibrosis. We hope this article will help clarify the pathogenesis of these diseases and propose a future direction for research.