ABSTRACT
Introduction C D 4+ T helper (Th) cells can be divided into three major subsets, Type-1, Type-2 and
Type-3 T regulatory (Treg), based upon the specific cytokines produced and the functional activities exhibited by each cell type. Type-1 Th cells produce interferon-y (IFN-y) and lymphotoxin (LT), which promote macrophage activation and the generation of cell-mediated immunity. Type-2 Th cells produce a variety of cytokines including IL-4, IL-5> and IL-13, and provide help for the maturation of B cells to immunoglobulin-secreting cells, thereby activat ing humoral defense mechanisms. In contrast to T h l and Th2 cells, however, T regulatory cells represent a unique and more heterogeneous population, which can express a variety of immune suppressive factors including cytotoxic T-lymphocyte antigen-4 (CTLA-4), transforming growth factor (TGF)-p, and/or IL-10.
