Characterization of antigen-specific naive T cells. (A) Six PA-reactive T cell lines isolated from a single donor were screened for their capacity to proliferate in response to pools of peptides spanning the PA sequence. Shown is the response of each cell line to the 12 pools. The pools were then deconvoluted and the peptide recognized by each cell line was identified (see Table S2). One representative experiment of two performed. (B) 18 KLH-specific T cell lines from six different blood donors were stimulated with increasing concentrations of KLH. (C) EC50 values were calculated as described in the text. Bar indicates median value. The experiment shown in B and C are representative of three different experiments, each performed with 10–18 KLH-specific T cell lines isolated from 3–6 different donors.