Immunohistological detection of human herpes virus 6 in formalin-fixed, paraffin-embedded lung tissues.

Human herpes virus type 6 (HHV-6) infection is widespread in healthy individuals. The only definite disease association is with exanthem subitum in infants though the virus has been linked with a variety of other diseases including interstitial pneumonitis in bone marrow allograft recipients. In order to investigate the role of HHV-6 in the latter disease we have developed an optimised staining method for the demonstration of specific antigen in routinely processed post-mortem tissues. Formalin-fixed, paraffin-embedded lung tissue from 8 immunocompromised patients who died from interstitial pneumonitis was subjected to immunoperoxidase staining with monoclonal antibodies against HHV-6, cytomegalovirus (CMV), and adenovirus, using a modified avidin-biotin complex (ABC) method. Staining for HHV-6 was obtained in 6 of the 8 patients studied and was present in pneumocytes and macrophages. CMV and adenovirus antigens were identified in 4 and 6 patients, respectively. Whilst the lung tissue of 6 patients contained more than one virus, there was no evidence of cross-reactivity between the monoclonal antibodies. We demonstrated that accurate localisation of HHV-6 using monoclonal antibodies is possible in post-mortem lung tissue and conclude that either HHV-6 alone or in combination with other viruses may play a role in the development of interstitial pneumonitis following bone marrow transplantation or chemotherapy.