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

Abstract

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 (T CM ) cells, effector memory T (T EM ) cells, and tissue resident memory T (T RM ) cells. T RM 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, T RM cells that reside in the skin can respond rapidly to pathogenic challenges. However, there is emerging evidence to support the vital role of T RM 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 T RM 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 T RM cells and share our perspectives on the biological characteristics of T RM cells in the recurrence of inflammatory skin disorders.

Immunological Memory of Psoriatic Lesions

“…The second type of TRM are CD4+ cells, which are less-known ones, and are located near the vessels in the dermis; they do not express CD103 and have a high proliferative capacity. They are responsible for defense against Leishmania and Candida albicans in the gut, lungs and reproductive system [24].…”

“…In contrast, TRM can produce granzyme B (serine protease), which can induce cellular apoptosis [23]. Moreover, IL-15 probably plays an important role in TRM cell survival [24].…”

“…However, after discontinuation of treatment, a rapid recurrence of lesions is usually observed (90% in the same location) [24]. The understanding of the psoriasis context and the role of TRM can explain the key issues associated with this disease: -the role in resistance to treatment and reactivation of changes in the same location [24]; -the role in the Koebner isomorphic symptom [24];…”

Dihydroartemisinin ameliorates psoriatic skin inflammation and its relapse by diminishing CD8+ T-cell memory in wild-type and humanized mice

“…T CM cells can also expand upon re-challenging in vitro and develop into Th17 cells 12 . On the other hand, resident T or resident memory T (T RM ) cells persist for long term in the skin and do not recirculate through the blood 13 , 14 . Previous studies have shown that T RM cells are enriched in both active and resolved psoriatic skin lesions 15 , 16 .…”

The nerve injuries interfere with the development of psoriasis

“…Researches in recent decades demonstrate that immune disorders play an important role in psoriasis development. 1 And applications of biological antibodies against cytokines with abnormal levels have improved conventional therapeutic effects. 2 On the other hand, immune cell activation alone might not account for some of the features in psoriasis, e.g.…”