Interleukin-18 enhances the production of interferon-gamma (IFN-γ) by allergen-specific and unspecific stimulated cord blood mononuclear cells

Background: IL-18 is a pleiotropic cytokine involved in the polarisation of T-cell response. This study was performed to determine whether or not IL-18 is detectable in phytohemagglutinin (PHA) or betalactoglobulin (BLG) stimulated supernatants of cord blood mononuclear cells (CBMC) and to study the in vitro effect of IL-18 on the interferon (IFN)-γ and IL-13 release of CBMC of healthy neonates. Methods: CBMC of neonates were isolated by Ficoll density centrifugation. The cytokines IFN-γ, IL-13 and IL-18 in the cell culture supernatants were measured using the ELISA technique following stimulation with a unspecific (PHA 20μg/ml) and an allergen-specific stimulus (BLG 25μg/ml). In order to study the in vitro effect of IL-18, CBMC were stimulated either with medium alone or with IL-18, IL-18+PHA and IL-18+BLG. Results: IL-18 levels in supernatants of CBMC were low and did not vary significantly between unstimulated and PHA or BLG stimulated cell cultures (median 21.4; 23.5 and 15.5pg/ml, respectively). IFN-γ and IL-13 levels were significantly higher in response to PHA and BLG (PHA: IFN-γ, 6154; IL-13, 4357; BLG: IFN-γ, 801; IL-13, 249pg/ml) compared to unstimulated cell cultures. The addition of IL-18 to PHA or BLG stimulated CBMC significantly enhanced the IFN-γ release (PHA: 6154; PHA+IL-18: 13474, p=0.0001; BLG: 801; BLG+IL-18: 1077, p=0.008). In comparison to incubation without IL-18, the release of IL-13 was invariable or even reduced, when CBMC were stimulated with PHA+IL-18 (4026, p=0.16) or BLG+IL-18 (124, p=0.0001) compared to stimulation of CBMC with PHA (4357pg/ml) or BLG (249pg/ml) alone. Conclusions: IL-18 is detectable in supernatants of CBMC. We observed a significant effect of IL-18+PHA as well as IL-18+BLG on IFN-γ release in vitro. Based on our findings we conclude that IL-18 could act as a strong TH1-inducing factor on stimulated CBMC also in vivo.