Allergic asthma and allergic dermatitis are chronic inflammatory diseases and are characterized by an accumulation of eosinophils at sites of inflammation. Eotaxin-1/CCL11 and eotaxin-3/CCL26 are members of the CC chemokine family, which are known to be potent chemoattractants for eosinophils. We observed that a human lung fibroblast, HFL-1 produces eotaxin-1 and -3 in response to TNF-alpha plus IL-4 stimulation, accompanied with NF-kappaB and STAT6 activation. We explored which signaling pathways are operative in the production of eotaxin-1 and -3 using several inhibitors. Eotaxin-1/CCL11 production was inhibited by a p38 mitogen-activated protein kinase (MAPK) inhibitor, SB203580, but not by the MEK (MAPK/ERK kinase) inhibitors, PD98059 and U0126. In contrast, eotaxin-3/CCL26 production was inhibited similarly by PD98059 as well as U0126 and SB203580. In addition, two proteasome inhibitors, N-acetyl-leucyl-leucyl-norleucinal (ALLN) and bortezomib with significant inhibitory activity on NF-kappaB activation, inhibited eotaxin-1/CCL11 production with IC50 8 microM for ALLN and IC50 16 nM for bortezomib. In contrast, eotaxin-3/CCL26 production was not inhibited significantly up to 10 microM of ALLN (IC50 16 microM) and up to 10 nM of bortezomib (IC50 11 nM), giving inhibition of eotaxin-3/CCL26 less sensitive than eotaxin-1/CCL11 production by the proteasome inhibitors. Synergistic inhibition was observed among lower doses of SB203580 and proteasome inhibitors, particularly in the eotaxin-1/CCL11 production. No such prominent synergism was found on the eotaxin-3/CCL26 production. The suppression of eotaxin family production by these inhibitors may be efficacious against allergic diseases.