T cell regulation of hematopoiesis.

It has long been known that thymus-derived lymphocytes (T cells) can produce cytokines that have powerful effects on hematopoiesis. All major classes of T cells--CD4 T helper cells, CD4 regulatory T cells, CD8 T cells, gammadelta T cells and NKT cells--produce a number of cytokines and chemokines that can modulate hematopoiesis. More recent research has shown that specific T helper cell types, such as Th1, Th2 and Th17 cells, with the development of each subset depending on distinct STAT proteins, have the potential to modulate the hematopoietic response in different ways. In a teleological sense, the overall orchestration of the immune response by T helper cells fits with the concept that T helper cells would modulate the production of cells of the innate immune system by regulating hematopoiesis. Here we will review the literature on how T cell subsets regulate hematopoietic cell differentiation, and discuss how this regulation may complement the specific function of the T cell type.