T Lymphocyte Plasticity in Autoimmunity and Cancer

Copyright © 2015 Nona Janikashvili et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. T lymphocytes are essential for the development and regulation of adaptive immune responses. Upon engagement of their specific antigen receptor in presence of appropriate costimulatory signals and specific cytokines, na¨ıve CD4+ and CD8+ T cells differentiate into specific effector or suppressor subsets exhibiting distinct phenotypic characteristics and functions. These specialized T lymphocyte subsets are distinguished by a dedicated transcription factor and cytokine expression profile. Beyond T helper 1 (Th1) and T helper 2 (Th2) cells, T helper 9 (Th9), T helper 17 (Th17), T helper 22 (Th22), T follicular helper (Tfh), regulatory T cells (Treg), and Type 1 regulatory cells (Tr1) have now been recognized as distinct subsets into the CD4+ T lymphocyte compartment. Similarly, advances have also been acquired regarding CD8+ cell subset diversity (Tc1, Tc2, Tc17, and CD8reg). Although some of these polarized T cell subpopulations remain stable and hardly transdifferentiate into other subsets, evidence has been provided that others, such as Th17 or Treg cells, display variable degrees of plasticity as demonstrated by their capability to be " reprogrammed " into different suppressor or proinflammatory effector T cells. T lymphocyte plasticity depends on microenvironmental mediators such as cytokines and chemokines which vary in nature and amount during the course of autoimmune diseases or the development of cancer. A better understanding of the fundamental mechanisms and the regulation of T lymphocyte adaptive plasticity is essential for a comprehensive characterization of the pathogenesis of immune mediated disorders and cancer immunosurveil-lance. The possibility to interfere with the process of T cell polarization may also open new therapeutic options. In this special issue, authors addressed topics related to the altered frequencies and functions of T lymphocyte subsets and the molecular and cellular mechanisms responsible for T cell lineage commitment, polarization, and reprogrammed adaptive responses in health and pathology. E. Ivanova and A. N. Orekhov provide an overview on the properties of T helper lymphocyte subsets and describe signaling networks, cytokines, transcription factors, and disturbances which can cause immune dysregulation, such as excessive inflammatory response in autoimmune diseases or enhanced immune tolerance to tumors. T. Caza and S. Landas summarize the epigenetic modifications of cytokine loci that determine CD4+ T cell lineage specifications and emphasize …