Granulocyte/macrophage colony-stimulating factor inhibits IL-12 productionof mouse Langerhans cells

We investigated the capacity of mouse Langerhans cells (LC) to produce IL-1 2, a central cytokine in a Th1 type of immune responses. We prepared purifi ed LC (>95%) from BALB/c mouse skin by the panning method using anti-I-A(d) mAb. An ELISA showed that purified LC spontaneously produced IL-12 p40, an d that its production was up-regulated following simultaneous stimulation w ith anti-CD40 mAb and IFN-gamma. Surprisingly, GM-CSF strikingly inhibited IL-12 p40 production by anti-CD40/IFN-gamma-stimulated LC (% inhibition = 9 7.0 +/- 0.9% at 1 ng/ml GM-CSF), Supernatants of 48-h cultured keratinocyte s (KC) also caused the inhibition of LC IL-12 p40 secretion, and this effec t was neutralized by anti-GM-CSF mAb. IL-1 alpha (1 ng/ml)-stimulated KC pr oduced much more GM-CSF than unstimulated KC (60.9 +/- 0.2 pg/ml vs 20.9 +/ - 1.7 pg/ml), and IL-1 alpha-stimulated KC supernatants strongly inhibited IL-12 p40 production by anti-CD40/IFN-gamma-stimulated LC (% inhibition = 8 9.4 +/- 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, T hese 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.