Detection of HHV-6 DNA by PCR amplification. The amplified products were subjected to electrophoresis and stained with ethidium bromide. (A) The 186-bp product amplified with primer pair 1 is seen in lanes 1, 3, and 4. (B) A nested PCR assay. A first round of amplification with primer pair 2 generated a 520-bp product seen in lanes 1, 3, and 4. A second round of amplification that was performed with nested primer pair 2′ and one-hundredth of the products of the first round of amplification generated a 258-bp product. (C) Variant determination of HHV-6 by PCR. Generation of a 553-bp product by PCR with primer pair 3 indicates the presence of HHV-6 variant B. The PCR products detected were all of the predicted sizes based on previous reports. Lane 1, HHV-6B–infected MT-4 cells as a positive control; lane 2, Akata cells as a negative control; lane 3, patient's original lymphoma cells; lane 4, Katata cells; lane M, φX174/HincII-cut DNA size marker.