Handwerger, Barry S.

Abstract The role of IL 1 in the activation of IL 4-producing murine T cell clones was investigated by using a calcium ionophore (ionomycin) or a phorbol ester (12-O-tetradecanoylphorbol 13-acetate; TPA) as T cell receptor-independent costimuli. The use of these pharmacologic agents to investigate IL 1-mediated T cell activation revealed two distinct mechanisms of activation. IL 1 in combination with ionomycin (iono/rIL 1) stimulated a proliferative response that was associated with the production of IL 4 as measured by lymphokine bioassay and mRNA studies. Furthermore, inhibition of this proliferative response with an anti-IL 4 monoclonal antibody or cyclosporine indicated that IL 4 functions as an autocrine growth factor. In contrast, IL 1 synergized with TPA (TPA/rIL 1) to induce proliferation in the absence of either IL 4 or IL 2 gene transcription or lymphokine secretion. The IL 4-independence of this activation mechanism was further supported by the failure of both anti-IL 4 antibodies and cyclosporine to inhibit the response. In addition, activation by TPA/rIL 1 caused no detectable alteration in cytoplasmic calcium levels. Both IL 4-dependent and IL 4-independent activation responses were associated with the expression of functional receptors for IL 2 as well as IL 4. Characterization of these activation responses suggests that the synergistic activity of IL 1 during T cell activation is multipotential. The nature of an IL 1-dependent T cell growth response, therefore, may vary depending on the balance of intracellular signals generated concurrently through the T cell receptor complex and other regulatory surface molecules.

Abstract The role of IL 1 in the antigen-specific activation of class II-restricted T lymphocytes was examined by using a model system consisting of cloned WEHI 5 B lymphoma accessory cells and class II-restricted, soluble antigen- or alloantigen-reactive T cell clones. The addition of exogenous recombinant IL 1 to the T cell cultures resulted in a significant enhancement of the antigen-specific T cell proliferation response, but at best, only small increases in IL 2 release. Goat IgG anti-IL 1 antibodies were added to the T cell cultures to assess their effect on T cell activation. The IL 1 enhancement of the T cell proliferation response was inhibited by the anti-IL 1 antibodies in a dose-dependent manner. In contrast, only modest levels (10 to 25%) of proliferation inhibition were observed in T cell cultures containing either WEHI 5 or splenocyte accessory cells but no exogenous IL 1. When the anti-IL 1 antibodies were added to primary mixed lymphocyte cultures stimulated by WEHI 5 cells in the absence of exogenous IL 1, no significant inhibition of proliferation was observed. A small but statistically significant proliferation inhibition was observed when anti-IL 1 antibodies were added to mixed lymphocyte reaction cultures stimulated by splenocytes. Two-color cytofluorometric analysis of the effects of IL 1 on antigen-activated T cell clones demonstrated that under suboptimal stimulation conditions, IL 1 stimulated a small but significant increase in the number of T cells bearing IL 2 receptors. In the presence of optimal numbers of WEHI 5 accessory cells, IL 1 enhanced T cell proliferation in the absence of a detectable increase in the number of T cells bearing IL 2 receptors, the number of IL 2 receptors per T cell, or the levels of IL 2 released. Finally, exogenous IL 1 can be added as late as 18 to 24 hr after culture initiation without significantly reducing its ability to enhance the T cell proliferation response. These data indicate that IL 1 has pleiotropic effects on murine T lymphocytes and can function to enhance T cell activation at multiple points during the activation sequence.

Abstract The activation requirements of alloreactive and antigen reactive murine T cells were examined by stimulating class II restricted T cell clones with monoclonal B lymphoma cells. One B lymphoma cell line (T27A) was found to stimulate IL 2 release from some alloreactive T cell clones without stimulating any significant T cell proliferation response. The same B lymphoma cells are capable of stimulating IL 2 release and proliferative responses from other T cell clones. Evidence is presented suggesting that B lymphoma cell stimulation of these T cell clones is largely IL 1 independent and that at least some T cell clones may require activation signals other than Ia, antigen, and IL 1. The addition of exogenous, purified IL 1 to the T cell activation assays was found to have a wide range of stimulatory effects on the proliferative responses of different T cell clones. The absence of comparable IL 1-induced stimulation of IL 2 secretion suggests that IL 1 primarily enhances antigen specific T cell proliferation through mechanisms other than acting as a co-stimulant for IL 2 release.