Cooperative effect of interferon‐γ and tumor necrosis factor‐α on the induction of the class II antigen‐associated invariant chain expression

Abstract

The regulation of the invariant chain (I_i) expression was studied in the human colon carcinoma cell line HT‐29 that constitutively expressed neither I_i nor class II antigens. Upon stimulation of HT‐29 cells with a combination of human recombinant tumor necrosis factor‐α (TNF‐α) and interferon‐γ (IFN‐γ), expression of mRNA and protein of the invariant chain were induced. In contrast, administration of TNF‐α or IFN‐γ alone had no effect. A delayed induction of I_i mRNA, which was first detected 10–12 h after stimulation, was observed; this suggests an indirect regulatory mechanism. Stimulation with both IFN‐γ and TNF‐α led to the co‐expression of class II antigens with the invariant chain. In order to study the genetic basis for this stimulation the murine invariant chain gene (800 bp 5′ flanking sequences and the structural gene) was transfected into HT‐29 cells and transfected cells were tested for the ability to respond to IFN‐γ and TNF‐α. Simultaneous application of both cytokines had a strong effect on the induction of the murine invariant chain. IFN‐γ alone had no effect and TNF‐α only marginally stimulates murine invariant chain expression. The transfection experiment indicates that the murine invariant chain gene construct contains the structural elements which are responsible for regulation with IFN‐γ and TNF‐α. We determined whether the cooperative effect of TNF‐α and IFNγ is also found in vivo. Stimulations of mice were performed with TNF‐α, IFN‐γ and a combination of both. The immunohistological analysis of kidney tissue sections revealed that TNF‐α had no effect on I_i and Ia expression. Upon IFN‐Y treatment a minor subset of renal tubules showed staining for Ii, and less prominently also for Ia. However, simultaneous application of both cytokines led a strong induction of both Ii and Ia antigens in renal epithelial cells, thus suggesting that this synergistic effect potentially occurs under physiological conditions.