HUMAN T-HELPER CELL-DIFFERENTIATION IS REGULATED BY THE COMBINED ACTION OF CYTOKINES AND ACCESSORY CELL-DEPENDENT COSTIMULATORY SIGNALS

We have developed an in vitro differentiation model for human Th cells to study the role of cytokines and accessory cell-dependent costimula tory signals in this process. Peripheral blood-derived CD4(+) ''naive' ' (CD45RA(+)RO(-)) T cells were stimulated in weekly intervals with im mobilized anti-CD3 mAb, accessory cells, and exogenous cytokines, and were analyzed for cytokine secretion pattern. With the B cell line JY (B7-1(+)B7-2(+)), as source of accessory cells, we could generate dist inct Th subsets. Coculture with the combination of recombinant human ( rh) IL-1 beta and rhIL-6 gave rise to Th0-like cells, which secreted l ow levels of IFN-gamma and IL-5. The addition of rhIL-12 led to the ge neration of Th1-like cells, which secreted high levels of IL-2, IFN-ga mma, TNF-alpha, and upon multiple stimulations, significant levels of IL-10. The presence of rhIL-4 induced Th2-like cells that secreted hig h levels of IL-5 and IL-13, but undetectable levels of IL-4. Only afte r stimulation with phorbol ester and calcium ionophore could these Th2 -like cells be induced to secrete significant levels of IL-4, indicati ng distinct stimulatory requirements for the induction of IL-5 and IL- 13 compared with IL-4. The B7-1-negative monocytic cell line U937 coul d only provide accessory cell-dependent costimulatory signals for the generation of Th1-like cells, while B7-1-transfected U937 cells acquir ed the capacity to provide costimulation for the generation of Th2-lik e cells. These results indicate a differential dependence on CD28-medi ated costimulation for the generation of human Th1-like and Th2-like c ells.