Precursor frequency of GPIIb/IIIa-reactive T cells in CD45RA⁺ or CD45RO⁺ T-cell subsets from ITP patients and controls. From 19 healthy donors (HD) and 25 ITP patients, the purified CD4⁺CD45RA⁺ and CD4⁺CD45RO⁺ T cells (2 × 10⁴/well) were seeded into 96-well plates along with autologous irradiated PBMCs (1 × 10⁵/well) and stimulated with trypsin-digested GPIIb/IIIa for 7 days. During the last 16 hours of incubation, the cells were pulsed with 1 μCi [³H]thymidine/well. Wells stimulated with antigens that had cpm greater than 3 times the mean cpm of negative control wells were identified as responders. The frequency of GP-specific T cells was calculated by dividing the number of responding wells by the number of seeded wells, multiplied by the number of cells per well. Data shown are the mean number of GPIIb/IIIa-reactive T cells per 10⁶ CD45RA⁺ versus CD45RO⁺ T cells plus or minus SD.