Deltaretrovirus PCR tested in serial dilutions of cell lines. Cell line DNA was diluted in genomic DNA from healthy individuals. A: cell line Mo T (HTLV-II-infected), B: cell line MJ (HTLV-I-infected), C: cell line BL3.1 (BLV-infected). First and last lane in every gel: φX174/Hae III size standard (QIAGEN, Hilden/Germany). No cell line harboring STLV-III, HTLV-III or HTLV-IV is currently available. All cell lines yield a PCR product of approximately 1.8 kB. A small sideband at 657 bp is visible which could serve as an internal control for DNA integrity.