IL-4 increases IL-2 production by T cells in response to accessory cell-independent stimuli.

Freshly prepared, highly purified T cells from naive mice failed to produce IL-2 in response to soluble anti-CD3 antibody or to Con A and produced only small amounts of IL-2 in response to anti-CD3 coated on the surface of microwells. IL-2 production in response to soluble anti-CD3 or to Con A required the addition of accessory cells. By contrast, the addition of IL-4 strikingly enhanced the production of IL-2 by plate-bound anti-CD3-stimulated T cells in the absence or the presence of added accessory cells. Furthermore, anti-IL-4 mAb inhibited IL-2 production by anti-CD3-stimulated T cells, which indicates that endogenously produced IL-4 was important in IL-2 production by T cells to plate-bound anti-CD3. The capacity of IL-4 to enhance and of anti-IL-4 to inhibit IL-2 production in response to plate-bound anti-CD3 was also observed with both unstimulated T cells and with T cells that had been previously stimulated with anti-CD3 antibody. When activated T cells were restimulated with anti-CD3, the effect of IL-4 in enhancing IL-2 production was detectable within 6 to 8 h after restimulation. The effect of IL-4 on IL-2 production was not due to prolongation of survival or to enhanced proliferation of T cells. Northern blot analysis showed that T cells treated with anti-CD3 plus IL-4 had more than 10-fold more IL-2 mRNA than did T cells treated with anti-CD3 plus anti-IL-4; this was observed within 6 h of stimulation under certain circumstances. The increased level of IL-2 mRNA by IL-4 was achieved without any change in message half-life, suggesting that IL-4 enhances transcriptional activation of the IL-2 gene in such cells. These results lead to the conclusion that IL-4 has a critical role in IL-2 production in response to accessory cell-independent stimuli (plate-bound anti-CD3 antibody), although it is not essential to IL-2 production in response to accessory cell-dependent stimuli (soluble anti-CD3 and Con A).