Source
Department of Biology, University of California, San Diego, La Jolla 92093.
Abstract
We have investigated the effects of TGF-beta on the in vitro development of different subsets of Th cells and find that addition of TGF-beta results in the generation of cell populations with distinct characteristics that resemble those of memory cells. Resting, short-lived CD4+ precursor T cells can be induced by mitogen stimulation to proliferate and differentiate in in vitro cultures and after 4 to 7 days will generate a population of cells that, when restimulated, synthesize and secrete high titers of a wide variety of lymphokines. It has been previously reported that the presence of the lymphokine IL-4 during in vitro culture results in the generation of a population of "effector" cells that can be rapidly induced by mitogen to synthesize and secrete high titers of IL-4, IL-5, IL-3, IFN-gamma, and granulocyte-macrophage-CSF. We find that TGF-beta added to CD4+ precursors, suppresses the development of IL-4/IL-5 secreting effectors and results instead in the development of cells secreting IL-2 and IFN-gamma. CD4 T cells generated in the presence of TGF-beta show little or no expression of CD45RB, in contrast to those developed in IL-4 (or in IL-2 alone) that express high surface densities of CD45RB. The kinetics of cell recovery also differs when TGF-beta rather than IL-4 is present during culture. Cultures of effectors generated in TGF-beta, initially have low cell recoveries but cells expand dramatically between 4 to 7 days in the presence of IL-2 whereas IL-4 induces optimum cell recovery at day 4 and cell recoveries decrease with further culture. The properties of cells grown in TGF-beta thus show several attributes in common with memory or highly differentiated CD4+ cells, i.e., IL-2 as a predominant cytokine, easy propagation and low expression of CD45RB. Therefore, we propose the hypothesis that TGF-beta favors the development of a population(s) of Th cells that is likely to give rise to memory cells although IL-4 favors development of a short-lived effector population that secretes Th2 lymphokines.