The effect of interleukin 4 (IL-4) and IL-13 on IL-6 and IL-1 beta production by human embryonic microglial cells and human peripheral blood monocyte cells (PBMC) was compared. IL-4 or IL-13 increase intra-cellular IL-6 mRNA and IL-6 titres in supernatants of microglial cells whereas they decreased IL-6 production by PBMC tested in the same conditions. IL-4 and IL-13 increased also IL-1 beta production by human microglial cells. Stimulations associating IL-4 or IL-13 and IL-1 beta had an additive effect on IL-6 production by microglial cells, whereas, in the same conditions, an inhibitory effect was observed in PBMC. In contrast, dexamethasone downregulated IL-6 production by microglial cells and PBMC. Finally, IL-1 receptor (IL-1r) type 1 and IL-1r type 2 were detected on human microglial cells but it was demonstrated that IL-13 and IL-4 acted as IL-6 inducers in human microglial cells independently of the IL-1/IL-1r pathway.