INDUCTION OF IL-12 P40 MESSENGER-RNA EXPRESSION AND IL-12 PRODUCTION OF MACROPHAGES VIA CD40-CD40 LIGAND INTERACTION

The mechanism of IL-12 production has been studied by stimulating macr ophages or B cell lines with LPS, Staphylococcus aureus, or phorbol di ester. However, since IL-12 plays an important role in the activation of T cells interacting with APC, it is important to study the mechanis m of IL-12 production induced by T helper cell-APC interaction. We and others have demonstrated that IL-12 is produced in cultures where Th1 cells are stimulated with Ag or APC. In the present experiments, we s tudied a role of CD40-CD40 ligand (CD40L) interaction in IL-12 product ion and obtained the following results: 1) incubation of normal Th1 cl one with APC in the presence of Ag induced IL-12 p40 and p35 mRNA accu mulation and IL-12 production, and the addition of anti-CD40L blocked the p40 mRNA accumulation and IL-12 production but not p35 mRNA accumu lation; 2) when Th1 clone from a CD40L-deficient mouse was used in the incubation, p35 mRNA accumulation was induced, but neither p40 mRNA a ccumulation nor IL-12 production was induced; 3) CD40L(+) Th1 clone, o r insect cell membrane expressing mouse CD40L, induced p40 mRNA accumu lation and IL-12 production but not p35 mRNA accumulation. These resul ts indicate that the CD40-CD40L interaction plays a critical role in I L-12 p40 mRNA accumulation and bioactive IL-12 production and that p35 mRNA accumulation was regulated via a different mechanism than CD40-C D40L interaction. Most of the cells producing IL-12 were Mac-1(+) macr ophages.