Comparison of specific serological assays for diagnosing human herpesvirus6 infection after liver transplantation

Cross-reactivity between human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7) antibodies and the reliability of specific serological assays wer e analyzed for 12 patients with concurrent HHV-6 and HHV-7 antibody respons es after transplantation with a liver from a living relative by using an im munofluorescence assay (IFA). A neutralizing antibody titer assay (NT) and an immunoblot assay (IB) designed to detect immunoglobulin M (IgM) antibody to the HHV-6 immunodominant 101-kDa protein were compared in the diagnosis of an active HHV-6 infection. A total of 9 of 12 patients demonstrated con current HHV-6 and HHV-7 antibody responses, including increased Ige titers and/or the presence of IgM by IFA, and were thus analyzed for cross-reactiv e antibody to heterologous virus. The average percentages of residual antib ody to HHV-6 and HHV-7 after absorption with HHV-6 antigen were 32.6% (rang e, 6 to 50%) and 55.6% (range, 35 to 100%), respectively. All 12 patients w ere subsequently analyzed for HHV-6 antibody by using IB and NT, IB detecte d IgM antibody to the 101-kDa protein in 75% (9 of 12) of the recipients. A significant rise in the NT antibody titer was detected in the same nine sa mples. However, HHV-6 DNA was detected by PCR in only five of nine plasma s amples collected from recipients with a specific serologic response against HHV-6.