Neuronal apoptosis in herpes simplex virus - 1 encephalitis (HSE)

Herpes simplex virus infections are encountered often due to their ubiquitous nature. Common sites involved include skin, mucous membrane, genitalia, eye and the nervous system. HSV infection of the central nervous system can be life threatening. Little is known about the pathogenesis of this cataclysmic disease, at the cellular level. Virus induced apoptosis may play a role in the molecular pathogenesis of encephalitis. This study aims to detect the presence of apoptosis: a) In the brain tissue obtained at autopsy from a patient who succumbed to Herpes simplex virus - 1 encephalitis (HSE) and b) In a human glioblastoma cell line (SNB 19). Wedge tissue samples were obtained from the inferior surface of the frontal lobe and fixed in buffered formalin. Tissue sections were stained with haematoxylin and eosin for histopathological analysis. An indirect immunoperoxidase assay was performed for the detection of HSV -1 antigen in the tissue sections. Apoptosis in the brain tissue was detected employing the TUNEL assay (Terminal deoxynucleotidyl Transferase (TdT) mediated deoxy Uridine Triphosphate Nick End Labeling) using a commerically available kit (TdT Fragel DNA fragmentation detection kit, Oncogene Research Products, CA). HSV-1 induced apoptosis of SNB 19 cells were detected in-vitro by: a) Membrane blebbing assay and b) Hoechst 33258 staining. Classical features of viral encephalitis including the presence of intranuclear inclusions, neuronal loss and perivascular cuffing were seen in the tissue sections. The immunoperoxidase assay revealed the presence of abundant viral antigen in the neurons, microglial and satellite cells. TUNEL assay revealed many apoptotic neurons, microglial and satellite cells. In-vitro assays showed evidence of HSV-1 induced apoptosis in the SNB 19 cell line. These results suggest that virus induced apoptosis may play a role in the molecular pathogenesis of HSE. Further studies are warranted to elucidate the role of HSV-1 induced apoptosis, especially employing cell lines of neuronal origin.