Comparison of in situ DNA hybridization (ISH) and immunocytochemistry for diagnosis of herpes simplex virus (HSV) encephalitis in tissue.

Formol-fixed and paraffin-embedded brain tissue of 33 cases of human necrotizing encephalitis was investigated for Herpes simplex virus (HSV) by immunocytochemistry with a polyclonal antiserum, and by in situ hybridization (ISH) with a biotinylated cDNA probe. HSV antigens (VA) were found in various types of cells in the cytoplasm, cellular processes and nuclei. Labelling by ISH was mostly restricted to nuclei and intranuclear inclusions but otherwise matched the distribution of VA. Eighteen of 25 acute cases had HSV antigen detectable by immunocytochemistry, and 18 of the acute cases contained HSV DNA detectable by our ISH technique. However, results differed somewhat between the techniques: three brains negative for VA showed hybridization, and other 3 VA-positive cases remained negative by ISH. Thus 21 brains with acute necrotizing encephalitis were labelled with one or both techniques. In 8 cases with a subacute course (duration of disease was longer than 1 month), HSV antigens were never detectable although 4 brains showed hybridization. All brains labelled by one or both techniques contained nuclear inclusions bodies. Only one case, of subacute course, with inclusion bodies remained unlabelled. Brain tissue of 11 controls, including cytomegalic inclusion body disease, was never labelled. These results demonstrate that immunocytochemistry and ISH are techniques of comparable sensitivity (72%) for detection of HSV in paraffin sections of acute necrotizing encephalitis brains; their combined use enhanced sensitivity, in our hands, to 84%. In cases with a disease course longer than one month, ISH seems to be the method of choice to demonstrate HSV in situ.