A common feature of some parasitic infections and allergic and atopic skin diseases is the involvement of Th2 lymphocytes and the dermal appearance of eosinophils (Eos). Because Th2 lymphocytes apparently do not release Eo attractants, we addressed the question of whether the Th2 cytokine IL-4 induces its production in dermal fibroblasts. We therefore stimulated fibroblasts with IL-4. HPLC investigation of supernatants revealed a single Eo chemotactic protein, which was purified to homogeneity giving a single 13-kDa band upon SDS-PAGE analyses. Peptide mapping with subsequent amino acid sequencing revealed an Eo-selective chemotaxin, which consists of a mixture of N-terminally truncated and O-glycosylated forms of the chemokine eotaxin. Other chemokines such as RANTES, MCP-3, MCP-4, or MIP-1α were not detected as Eo chemotaxins under these conditions. Using reverse transcriptase-PCR techniques, we found that IL-4 dose and time dependently induces eotaxin mRNA in dermal fibroblasts. Stimulation with IL-4 and TNF-α caused a 10-to 20-fold increase of the release of three biochemically different eotaxin forms, each consisting of a mixture of N-terminally truncated and O-glycosylated variants having the same backbone amino acid sequence but different specific activities. Our findings support the hypothesis that eosinophil recruitment seen in IL-4-mediated skin reactions, at least in part, may be due to Th2 cytokine-mediated induction of eotaxin in dermal fibroblasts.