Markers of Th1 polarized Th17 cells (literature review)

Abstract

T helpers (Th) producing IL-17 (Th17) have high plasticity and under the influence of external conditions are able to redifferentiate into cells with a different phenotype, primarily in Th1-lymphocytes, forming a population that combines the characteristics of both Th17 and Th1 and has a high pro-inflammatory potential, as well as a unique ability to overcome histohematic barriers. These cells are currently assigned a key role in the pathogenesis of many inflammatory diseases, including autoimmune ones: they account for up to half of the lymphocytes present in infiltrates of inflamed tissues. The paper discusses the reasons for the increased plasticity of Th17 cells in comparison with the main T helper populations (Th1 and Th2) and considers in detail the mechanisms of formation of IFNγ producing Th17, taking into account not only the redifferentiation of mature Th17, but also possible alternative pathways, in particular, Th1 cell redifferentiation or naive CD4+T lymphocytes direct differentiation into cells with an intermediate Th1/Th17 phenotype. The main inducers of differentiation of IFNγ producing Th17 cells and the reversibility of this process are also discussed. Particular attention is paid to the methods for identifying Th1 polarized Th17 cells: this population is heterogeneous, and its size significantly depends on the type of markers used to characterize these cells – Th1/Th17-associated transcription factors, key cytokines, as well as chemokine receptors and other membrane molecules. As a result, the data in the works on this problem are poorly comparable with each other. The unification of approaches to identifying a population of Th1 like Th17 cells will solve this problem and make it possible to use an assessment of the size and activity of such a population as diagnostic or prognostic markers.