Enhanced proliferation of murine T cell lines following interaction of poly(Glu60,Phe40) (GPhe) and antigen-presenting accessory cells. II. The role of accessory cells and cytokines in the activity of GPhe on antigen-independent proliferation.

Our previous study (1) demonstrated the "cytokine-like" activity of poly(Glu60,Phe40)(GPhe) in augmenting the antigen-dependent proliferation of a variety of long-term murine T cell lines, particularly the bulk, BALB/c anti-poly (Glu36,Lys24,Ala40) (GLA), interleukin-4-producing, DCL-2 T cell line. GPhe was found to also augment the antigen-independent proliferation of DCL-2 in response to exogenous cytokines ([interleukin(IL)-2 +/- IL-1] in most experiments). Such exogenous cytokine-driven proliferative responses of DCL-2 were used to investigate further the role of accessory cells and of various soluble factors in the action of GPhe. GPhe did not act as a direct mitogen for T cells, rather it acted in a costimulatory fashion, requiring the presence of plastic-adherent accessory cells and a T cell growth factor (either IL-2 or IL-4). In the presence of accessory cells and exogenous IL-2, augmentation of antigen-independent DCL-2 proliferation by GPhe or by IL-1 depended upon the induction of autocrine IL-4 production. However, GPhe also augmented the response of these cells in the presence of exogenous IL-4 (+/- IL-2, +/- IL-1), and exogenous IL-4 added in combination with exogenous IL-2 (+/- IL-1) failed to mimic the GPhe effect, suggesting that another signal was involved in the mechanism of action of GPhe. The ability of allogeneic accessory cells to interact with GPhe to augment proliferative responses suggested that either a soluble factor or an unusual non-MHC-restricted cell-cell interaction provided this signal. In the presence of uv-irradiated accessory cells, DCL-2 proliferation was enhanced over that observed in the presence of non-uv-treated accessory cells, mimicking the GPhe effect, and interaction of GPhe with uv-irradiated accessory cells did not result in further enhancement of DCL-2 cytokine-driven proliferation. Using monoclonal antibodies which could block the function of IA or CD4 molecules, these cell-surface "adhesion" molecules were shown not to participate in the activity of GPhe. By the addition of recombinant cytokines, neutralizing antibodies, or indomethacin, the mechanism of action of GPhe was also shown not to be dependent upon IL-1, IL-6, IL-7, TNF alpha, or prostaglandin production by accessory cells. However, the presence, individually, of some of these factors (IL-1, IL-7, or prostaglandins) could influence to a variable degree the magnitude of the GPhe effect.