T lymphocytes have been implicated in controlling the recruitment of eosinophils into the lung in murine models of allergic asthma. The mechanism by which T cells assist in the recruitment of eosinophils to the lung in these models is not completely understood. We hypothesized that eosinophil-active chemokines might be regulated by antigen (Ag)- induced T cell activation in vivo and thereby mediate T cell-dependent eosinophil recruitment. To test this hypothesis, we examined the effect of an anti-CD3 mAb on Ag-induced pulmonary eosinophilia and correlated this with the expression of three eosinophil-active chemokines: eotaxin, macrophage inflammatory protein (MIP)-1 alpha, and RANTES. We found that Ag-induced pulmonary eosinophilia was associated with the induction of eotaxin and MIP-1 alpha, but not RANTES mRNA. Prechallenge treatment with anti-CD3 mAb inhibited eotaxin, but not MIP-1 alpha and RANTES mRNA induction, and significantly reduced eosinophil accumulation in the lung. In addition, Ag-specific antibody responses and mast cell degranulation after Ag challenge in sensitized mice were not affected by T cell elimination, and were not sufficient to induce the expression of eotaxin and cause pulmonary eosinophilia. These findings suggest that eotaxin is one of the molecular links between Ag- specific T cell activation and the recruitment of eosinophils into the airways.