B19-Specific CD8⁺ T Cells Secrete IFNγ Ex Vivo, Proliferate, and Show Cytolytic Function In Vitro

<div><p>(A) Left panel shows that PBMCs from acutely infected patient O1 secrete IFNγ ex vivo after 18 h of FYTPLADQF peptide stimulation. Negative control (zero spots) and two peptide-stimulated wells from an ELISpot plate are shown. Numbers represent IFNγ-secreting cells per 250,000 PBMCs. Right panel shows A24 FYT tetramer staining of PBMCs at same time point, displaying the number of tetramer-positive cells expressed as a percentage of CD8⁺ T cells.</p> <p>(B) Tetramer staining of patient S2\′s PBMCs ex vivo (left) and after short-term TEADVQQWL peptide stimulation in vitro (right).</p> <p>(C) Ex vivo IFNγ ELISpot results for remotely infected individual OR3. Mean and standard deviations of triplicates are shown. Cells were stimulated for 18 h with no peptide, GLCPHCINV, or TEADVQQWL.</p> <p>(D) ⁵¹Cr release assay using HLA-A2-restricted GLCPHCINV-specific CTLs from individual OR1. PBMCs were stimulated for 14 d with GLCPHCINV peptide and cytolysis was tested against HLA-A*0201-transfected LBL.721.220 target cells at various effector-to-target-cell (E:T) ratios.</p>