Responses to VP1/2 peptides can be detected by ex vivo IFN-γ ELISPOT assays for acute but not remote B19 infection. (A) Ex vivo ELISPOT assay carried out on PBMCs from patient O22 (HLA-A 1,24; HLA-B 8,40; HLA-C 2,7; DRB1 15,3; DRB5,3; DQB1 2,6) at 4 weeks post-symptom development. Cells were stimulated with VP1/2 peptide pools and a B19 CD8+ T-cell epitope HLA-A2 LLMTDFEQV. (B) Ex vivo ELISPOT assay of PBMCs from remotely infected individual OR1. Cells were stimulated with VP1/2 peptide pools and the EBV HLA-A2 GLCTLVAML peptide (as a positive control). Triplicate estimations are displayed. The cutoff for a positive result is the result for the negative control plus 2 standard deviations (horizontal line).