Granulocyte/Macrophage Colony-Stimulating Factor Inhibits IL-12 production of Mouse Langerhans Cells

Abstract We investigated the capacity of mouse Langerhans cells (LC) to produce IL-12, a central cytokine in a Th1 type of immune responses. We prepared purified LC (>95%) from BALB/c mouse skin by the panning method using anti-I-Ad mAb. An ELISA showed that purified LC spontaneously produced IL-12 p40, and that its production was up-regulated following simultaneous stimulation with anti-CD40 mAb and IFN-γ. Surprisingly, GM-CSF strikingly inhibited IL-12 p40 production by anti-CD40/IFN-γ-stimulated LC (% inhibition = 97.0 ± 0.9% at 1 ng/ml GM-CSF). Supernatants of 48-h cultured keratinocytes (KC) also caused the inhibition of LC IL-12 p40 secretion, and this effect was neutralized by anti-GM-CSF mAb. IL-1α (1 ng/ml)-stimulated KC produced much more GM-CSF than unstimulated KC (60.9 ± 0.2 pg/ml vs 20.9 ± 1.7 pg/ml), and IL-1α-stimulated KC supernatants strongly inhibited IL-12 p40 production by anti-CD40/IFN-γ-stimulated LC (% inhibition = 89.4 ± 1.4%). A bioassay using an IL-12-dependent T cell line demonstrated the correlation of the level of IL-12 p40 with the bioactivity of IL-12. These results provide important implications for the pathogenesis of atopic dermatitis, which involves the participation of LC and KC with the capacity to produce IL-12 and GM-CSF, respectively.