['The essential role of Th cells and T cell cytokines in eosinophilic inflammation has been established.', 'To determine whether Th cells are sufficient for the development of airway eosinophilic inflammation, ovalbumin-reactive murine Th clones were established and infused into unprimed mice.', 'Eosinophilic infiltration into the lung was induced upon antigen inhalation in parallel with the rise in bronchoalveolar lavage fluid (BALF) eosinophil peroxidase activity. Neither IgG, IgA, nor IgE antibodies were present in this model. Pathological examination showed swelling and desquamation of epithelial cells, mucous plugs, and goblet cell hyperplasia, all of which well resemble human asthma. Fluorescent probe labeled Th clones migrated into the lung prior to the eosinophil accumulation. Bronchial hyperresponsiveness (BHR) was clearly induced upon antigen inhalation. Anti-IL-5 monoclonal antibody abrogated the responses. Dexamethasone and cyclosporin A suppressed cytokine production by Th cells both in vitro and in vivo, BALF eosinophilia, and BHR. The number of eosinophils recovered in the BALF correlated with the intensity of BHR.'] Do cloned Th cells confer eosinophilic inflammation and bronchial hyperresponsiveness?