ACANTHAMOEBA-SPECIFIC HUMAN T-CELL CLONES ISOLATED FROM HEALTHY-INDIVIDUALS

T-cell responses to pathogenic free-living amoebae, Acanthamoeba sp., were analyzed in healthy Japanese individuals. Of 20 healthy subjects, 10 (50%) showed significant proliferative responses of peripheral blo od mononuclear cells to the soluble amoebic antigens in vitro. The ant igens used were not mitogenic, and no evidence of amoebic superantigen s was available. We established human T-cell clones reactive to Acanth nmoeba, all of which were CD3- and CD4-positive, CD8-negative, and TCR -alpha beta-positive. We isolated two strains of Acanthnmoeba from two patients, one from a patient with meningoencephalitis (CSF strain) an d the other from a patient with keratitis (K strain). Of 13 clones, 11 were reactive to the K-strain as well as to the CSF-strain antigen un der human leukocyte antigen (HLA)-DR restriction, whereas the other tw o were specific for the K-strain antigen. All but one clone tested sho wed TH1-equivalent functions because these cells produced interferon ( IFN)-gamma in response to the amoebic antigen but produced no detectab le level of interleukin 4 (IL-4). These results suggest that immunocom petent hosts might have acquired protective immunity mediated by Acant hamoeba-specific T-cells during natural sensitization.