IL-17-Producing Regulatory T lymphocytes - Suppressors or Effectors?

Regulatory T (Treg) lymphocytes are a T helper population that controls the intensity of the immune response and maintains immune tolerance by selectively suppressing the activity of effector T lymphocytes. Treg cells are unstable and show high plasticity towards effector T helper populations, and the most common variant is Treg redifferentiation into T helpers producing interleukin-17 (IL-17 (Th17)). Although their formation has been confirmed by many studies in vivo and in vitro, Treg cells remain poorly understood in terms of their functional activity. The latter is yet fundamentally important for two major reasons. Firstly, an increase in the population of IL-17-producing Tregs has been identified for a number of diseases, raising the question of how these cells are involved in the development of pathologies. Secondly, understanding and predicting the behavior of Tregs in a pro-inflammatory environment promotes their therapeutic use. This review article analyzes the functional consequences of the redifferentiation of Treg cells into Th17.