Tissue-resident memory T cells and their biological characteristics in the recurrence of inflammatory skin disorders.

The skin is the largest organ of the body. The establishment of immunological memory in the skin is a crucial component of the adaptive immune response. Once naive T cells are activated by antigen-presenting cells, a small fraction of them differentiate into precursor memory T cells. These precursor cells ultimately develop into several subsets of memory T cells, including central memory T (TCM) cells, effector memory T (TEM) cells, and tissue resident memory T (TRM) cells. TRM cells have a unique transcriptional profile, and their most striking characteristics are their long-term survival (longevity) and low migration in peripheral tissues, including the skin. Under physiological conditions, TRM cells that reside in the skin can respond rapidly to pathogenic challenges. However, there is emerging evidence to support the vital role of TRM cells in the recurrence of chronic inflammatory skin disorders, including psoriasis, vitiligo, and fixed drug eruption, under pathological or uncontrolled conditions. Clarifying and characterizing the mechanisms that are involved in skin TRM cells will help provide promising strategies for reducing the frequency and magnitude of skin inflammation recurrence. Here, we discuss recent insights into the generation, homing, retention, and survival of TRM cells and share our perspectives on the biological characteristics of TRM cells in the recurrence of inflammatory skin disorders.