Figure 9. Schematic showing our proposed model of the immunosuppressive properties of ATL cells.

(A and B) ATL cells exert their immunosuppressive function by 2 mechanisms. (A) ATL cells acquire the Treg phenotype. ATL cells upregulate coinhibitory molecules (CTLA4, LAG3) to impair the maturation of APCs and reduce costimulatory signals required for complete T cell activation. They also upregulate CD25, leading to an increased consumption of IL-2, which reduces the amount of IL-2 available for effector T cell proliferation and activation. (B) ATL cells act as tolerogenic APCs. They upregulate HLA class II for antigen presentation, but since these ATL cells lack costimulatory signals, the target T cells are not activated, leading to T cell unresponsiveness and anergy.