Suppression of IL-12 Production by Soluble CD40 Ligand: Evidence for Involvement of the p44/42 Mitogen-Activated Protein Kinase Pathway

Abstract

IL-12 is a key cytokine in skewing immune responses toward Th1-like reactions. Human monocytes/macrophages produce high amounts of bioactive IL-12 when a priming signal (IFN-γ or GM-CSF) precedes a second signal (e.g., LPS). We and others have previously shown that preincubation with LPS before this stimulation procedure can efficiently and selectively suppress the production of IL-12 by human monocytes. In this study, we show that an almost complete suppression of IL-12 production can also be observed after preincubation of monocytes with costimulatory cell surface molecules that bind to members of the TNFR superfamily (CD40 ligand, TNF-related activation-induced cytokine (TRANCE)). The suppression of IL-12 was observable on the mRNA and protein levels and was not due to endogenous production of known IL-12 antagonists (i.e., IL-10, IL-4, and PGE2), to an increased number of cells undergoing apoptosis, nor to down-regulation of the IFN-γ or CD40 receptor. Cell surface expression of the costimulatory molecules CD80 and CD86 was not reduced by the preincubation procedure, and only a moderate reduction of IL-6 production was observed. Several studies have identified signal transduction pathways that are activated by CD40 signaling, including activation of mitogen-activated protein kinases. The presence of the extracellular signal-related kinase-specific mitogen-activated protein kinase kinase 1/2-specific inhibitors PD98059 and U0126 abrogated suppression induced by sCD40 ligand or other second signals. This indicates that activation of extracellular signal-regulated kinase 1/2 contributes to the underlying mechanism of IL-12 suppression. This mechanism may be relevant in other inflammatory responses and may help to develop therapeutic strategies in Th1-mediated diseases.

Pathological Role of Large Intestinal IL-12p40 for the Induction of Th2-Type Allergic Diarrhea

“…At the present time, we cannot offer any specific explanation for this distinct localization of IL-12p40. However, an interesting possibility would be that the expression of negative regulators for IL-12, including sCD40L and IL-10R, 14,43 could differ between the small and large intestine. To support this possibility, epithelial cells have been shown to express CD40 and IL-10R.…”

Histamine H4 Receptor Stimulation Suppresses IL-12p70 Production and Mediates Chemotaxis in Human Monocyte-Derived Dendritic Cells

“…4) in MoDC, we decided to investigate the MAPK pathway as a potential pathway induced by the H4R that is able to block IL-12p70 production (31). U0126, an inhibitor of AP-1 transactivation thought to act specifically at the level of the MEK1/2, preventing the phosphorylation of ERK1/2, rescued H4R-induced but not H2R-induced IL-12p70 suppression.…”

“…6a). For suppression of IL-12p70 production, the MAPK pathway was suspected (31), because the H4R is a G␣ i/o -coupled receptor (7). Such receptors have been reported to activate MAPK pathways, and activation of MAPK pathways has been reported to suppress IL-12p70 production (31).…”

“…For suppression of IL-12p70 production, the MAPK pathway was suspected (31), because the H4R is a G␣ i/o -coupled receptor (7). Such receptors have been reported to activate MAPK pathways, and activation of MAPK pathways has been reported to suppress IL-12p70 production (31). Indeed, preincubation of MoDC with U0126, an inhibitor of MEK 1/2 that blocks the phosphorylation of ERK1/2, rescued IL-12p70 suppression via the H4R-mediated signaling but not via the H2R-mediated response (Fig.…”

“…For quantitative analyses, the LightCycler relative quantification software (Roche) was used that is designed to determine exact efficiency corrected relative nucleic acid concentration, normalized to a calibrator sample. Amplification of the ␤-actin gene was performed in parallel to amplification of H3R and H4R as previously reported (11,31).…”