Interleukin-18 and Interleukin-12 Synergize to Stimulate the Production of Vascular Permeability Factor by T Lymphocytes in Normal Subjects and in Patients with Minimal-Change Nephrotic Syndrome

Abstract

Background/Aim: In a previous study, we reported that interleukin (IL)-12 could upregulate the production of vascular permeability factor (VPF) derived from activated human peripheral blood mononuclear cells. Since IL-18, a novel immunoregulatory cytokine with potent interferon-γ inducing activities, has been shown to be a strong cofactor for T helper type 1 cell development, we tested the hypothesis that IL-18 in combination with IL-12 can act synergistically to modulate the production of VPF. Methods: For this purpose, T cells were isolated from heparinized venous blood, stimulated with concanavalin A, and incubated in the presence of IL-18 or IL-12, and the production of VPF was determined by the method of Lagrue. Results: There was a significant increase in VPF production from concanavalin A-stimulated T cells following incubation with IL-18 or IL-12. More importantly, the combination of the cytokines was found to give a potent synergistic stimulation of VPF by concanavalin A-activated T cells from normal subjects. To determine the specificity of the stimulatory effect, neutralizing anti-IL-18 and anti-IL-12 antibodies were preincubated with IL- 18 and IL-12, respectively, prior to the addition of responder cells. The antibodies completely inhibited the effects of IL-18 and IL-12. Thus, these data show that IL-18 can synergize with IL-12 to selectively increase the production of VPF from T cells. The present study further demonstrates that IL-18 and IL-12 are in fact acting in synergy in patients with minimal-change nephrotic syndrome. Conclusions: Taken together, our results indicate that both IL-18 and IL-12 contribute to the VPF production in vitro and suggest that they play key roles in the complexity of cytokine regulation in the pathophysiology of VPF.