24. Which of the following statements about the mechanisms and characteristics of CD4+ regulatory T (Treg) cellsis NOT correct? (A) Treg cells are primarily known for their role in immune suppression through cytokine secretion and cell-cell interactions. (B) Treg cells express high levels of CD28, which competes with CD28 on effector cells for binding to B7 molecules on antigen-presenting cells, thereby inhibiting T cell activation. (C) Treg cells secrete perforin and granzyme A/B to kill target cells. (D) The stability and suppressive function of Treg cells in peripheral tissues can be influenced by the local cytokine environment including the presence of IL-6 and TGF-β. (E) Treg cells can convert into effector T cells under certain inflammatory conditions, contributing to immune responses.