Quantitative analysis of herpesvirus load in the lymph nodes of patients with histiocytic necrotizing lymphadenitis using a real-time PCR assay.

The cause of histiocytic necrotizing lymphadenitis (HNL) has been ascribed to viral infection, but its pathogenesis still remains unknown. Real-time PCR assays are useful not only for their sensitivity of detection but also for the quantitation of viral DNA with a wide linear range. We accordingly used this technique to estimate for each patient the viral load of the following members of the herpesvirus family: Epstein-Barr virus (EBV), cytomegalovirus (CMV), and human herpesvirus (HHV) types 6, 7, and 8. Samples of patients diagnosed as reactive lymphadenopathy (RL) were included for control. Thirty percent (6/20 cases) and 63% (12/19 cases) of the HNL and RL patients were positive for EBV, and the mean of the detectable EBV viral load of the HNL and that of the RL patients were 463 and 355 (copies/μg DNA), respectively. By in situ hybridization, EBV-encoded RNA could be detected in the lymph tissue samples with more than 14.3 copies/μg of EBV DNA. No significant difference was detected between the number of HNL patients with HHV6 DNA (3/20, 15%) or HHV7 DNA (2/20, 10%) and RL controls. CMV and HHV8 were not detected in the DNA from any patient. In this study, we were unable to definitively identify the causative herpesvirus for HNL; however, 1 HNL case had an extremely large copy number of HHV6-DNA and displayed positive immunostaining for the HHV6 early/late antigen in lesional areas of the node, suggesting that HHV6 infection may be associated with some cases of HNL.