However, the Finnish group found when studying HFRS caused by PUUV that IFN-γ ELISPOT assays using PBMCs obtained in the acute stage of the disease hugely underestimated the frequency of peptide-specific T cells compared to HLA/peptide tetramer staining probably due to activation induced apoptosis of these peptide-specific T cells during incubation with the peptides for the assay [20]. Here, IFNG is linked to hemorrhagic fever with renal syndrome.