Titration of STAT5 phosphorylation response to IL-7 and IL-15. (A-B) Mean results from 11 post-IM patients (closed symbols) and 18 healthy carriers (open symbols) in experiments assaying cytokine-induced STAT5 phosphorylation after exposure to the indicated doses of (A) IL-7 or (B) IL-15. Results are expressed as the percentage of EBV tetramer-positive cells (left panels) or total CD8⁺ cells (right panels) showing STAT5 phosphorylation. Data on EBV-specific populations represent cumulative results obtained with 4 tetramers all specific for EBV lytic cycle epitopes; similar results were obtained with 5 latent epitope-specific tetramers. (C) STAT5 phosphorylation in assays conducted on purified CD8⁺ populations (left panel) and on CD14-depleted PBMC populations (right panel). Representative results are shown from 1 of 5 experiments comparing post-IM patient and healthy carrier responses to the indicated doses of IL-15; results are expressed as the percentage of total CD8⁺ T cells showing STAT5 phosphorylation.