Herpes simplex virus antigen detection in human acute encephalitis: an immunohistochemical study using avidin-biotin-peroxidase complex method.

Autopsy specimens from six patients with clinically diagnosed herpes simplex virus (HSV) encephalitis were studied. Since immunocytochemistry has been reported to be a more reliable and successful method to identify HSV as the etiologic agent, antitype 1 HSV (HSV1) and antitype 2 HSV (HSV2) and the avidin-biotin-peroxidase complex (ABC) method were applied to brain paraffin sections. Positive immunostaining was observed in front-orbital, mediobasal temporal lobes, cingulate gyrus, and insula. The staining was bilateral but predominant on one side. In neurons, the cytoplasmic staining was prominent in perikarya and processes, less often observed in nuclei, rarely seen in nuclear inclusions. The positive staining was intense in oligodendrocytes and macrophages, in both nuclei and cytoplasm. In two cases astrocytic processes were stained strongly. Perivascular lymphocytes were always negative. Positive reactions were obtained with both anti-HSV1 and anti-HSV2 but weaker with anti-HSV2. This results suggests that, because of its high sensitivity, ABC method permits viral antigen detection not feasible with other methods. However, this method lacks of accuracy for HSV typing mainly because of probable antigens changes resulting from tissue processing.