Pathogenic role of tissue-resident memory T cells in autoimmune diseases

The tissue-resident memory T (T_RM) cells constitute a newly identified subset of memory T cells which are non-circulating and they persist for long-term in epithelial barrier tissues, including skin, lung, gastrointestinal tract and reproductive tract, and in non-barrier tissues, including brain, kidney, pancreas and joint. These cells provide rapid on-site immune protection against previous exposed pathogens in peripheral tissues. There cells are transcriptionally, functionally and phenotypically distinguished from circulating effector memory T cells. In addition to their protective functions, increasing evidence reveals that autoreactive and/or aberrantly activated T_RM cells may be involved in the pathogenesis of autoimmune disorders such as psoriasis and, as recently reported, may contribute to vitiligo, autoimmune hepatitis and rheumatoid arthritis. Therefore, this review aims to summarize the current progress in the biology of T_RM cells, such as the newly identified T_RM markers, upstream regulators, and the functions of T_RM cells. We also discuss the contributions of T_RM cells to the development of autoimmunity to broaden our understanding of autoimmune diseases and to provide novel potential therapeutic strategies for these diseases.