Double-edged sword: rd T cells in mucosal homeostasis and disease

Abstract

The mucosa is a tissue that covers numerous body surfaces, including the respiratory tract, digestive tract, eye, and urogenital tract. Mucosa is in direct contact with pathogens, and & gamma;& delta; T cells perform various roles in the tissue. & gamma;& delta; T cells efficiently defend the mucosa from various pathogens, such as viruses, bacteria, and fungi. In addition, & gamma;& delta; T cells are necessary for the maintenance of homeostasis because they select specific organisms in the microbiota and perform immunoregulatory functions. Furthermore, & gamma;& delta; T cells directly facilitate pregnancy by producing growth factors. However, & gamma;& delta; T cells can also play detrimental roles in mucosal health by amplifying inflammation, thereby worsening allergic responses. Moreover, these cells can act as major players in autoimmune diseases. Despite their robust roles in the mucosa, the application of & gamma;& delta; T cells in clinical practice is lacking because of factors such as gaps between mice and human cells, insufficient knowledge of the target of & gamma;& delta; T cells, and the small population of & gamma;& delta; T cells. However, & gamma;& delta; T cells may be attractive targets for clinical use due to their effector functions and low risk of inducing graft-versus-host disease. Therefore, robust research on & gamma;& delta; T cells is required to understand the crucial features of these cells and apply these knowledges to clinical practices. A small population of highly active immune cells known as & gamma;& delta; T cells protect mucosal tissue, which lines interior body parts that contact the exterior (such as lungs, mouth, and stomach) against pathogens, but can also cause diseases. Mucosal surfaces, with their high pathogen exposure, require especially good immune protection. Heung Kyu Lee and co-workers at the Korea Advanced Institute of Science and Technology, Daejeon, South Korea, have reviewed the helpful and harmful effects of these little-studied cells. These & gamma;& delta; T cells guard against viruses, bacteria, and fungi, help determine which microbes inhabit our bodies, and even play roles in pregnancy. On the other hand, they can be involved in autoimmune diseases. Their ease of transplantation and high activity make them promising candidates for clinical applications, and trials in cancer treatment are underway.